I noticed that there still wasn't a guide for 10/20s up yet, so I'll put something up here. I've uploaded 2 separate completions to youtube now.
Recorded wins using this or similar strat:
Myself: 2
Other youtubers: 1+

Disclaimer:
This is not a practically guaranteed way to beat 10/20s, unlike my guide for FNAF1 4/20s.
You could beat 10/20s in <2 hours with this method, and then never beat it again, or you could never beat it in the first place. Beating 10/20 takes a lot of luck & persistance unless someone comes up with a surefire method for beating it. If you do attempt 10/20s, don't go into it expecting to beat it- however, it is possible and anyone can do it.

10/20 completion (no moving challenge) 14/11/2014 10 am GMT
https://www.youtube.com/watch?v=L8NDvWbbXtg

10/20 completion 17/11/2014 by Taste Gaming, independently came up with same strategy
https://www.youtube.com/watch?v=f_Hu82wFGRo

10/20 completion 18/10/2014 by Aussie Gamer, https://www.youtube.com/watch?v=krNvWuW1QLw

completion 20/11/2014 after a weeks break (checking for Toy Bonnie when Music Box is wound up)
10/20
both parts: http://www.twitch.tv/dragondave17/c/5532105
part 1: https://www.youtube.com/watch?v=6BjXIJo2QX0
part 2: https://www.youtube.com/watch?v=PcUi2fmBqFo

original completion The victory run only 14/11/2014 10am GMT
both parts: http://www.twitch.tv/dragondave17/c/5532053
part 1: https://www.youtube.com/watch?v=iHxCI2G6VAs
part 2: https://www.youtube.com/watch?v=cFpWrh-VWZU


With the first completion on the same day it was originally completed, and the second completion today as of writing, I can confirm that this method still works in version 1.031, at least for me.


Basic method (repeat):
Wind 7 times
Mask on/off
Flash
Left vent light
Mask if necessary (repeat previous 2 steps of flash+vent if you mask)
Flash-cam


Each step explained with italics
Setup: Flash-Cams-Prize Corner(Cam 11)

Method:
Loop (from Cams):
Wind 7 times unless pulled off cam - Ignore Mangler's static
It's enough wind to survive multiple consecutive attacks & still have time for Foxy
I haven't fully tested winding more- Foxy may kill you, or not
Mask on/off
Will save you from flashing Golden Freddy, and mask will stay on if being attacked right away
Flash
Prevents Foxy from killing you, even if the hallway is blocked due to movement
Left vent light
BB is autokill if you go on cams when he's there. Toy Chica is around 50/50 kill chance
Mask on if
1. BB or Toy Chica is in vents
or 2. You heard Mangler while on cams or presently
or 3. You were attacked briefly, then it stopped. Often a sign you need to remask for Toy Bonnie
BB/TC as above. Mangler is autokill if you go on cams when there is static. TB can kill with this method, but the chance seems much lower after 2am. You could sweep right vent if you wanted.
Flash and left vent light again if you masked
You won't want BB/TC or Foxy to catch you out
Flash-cam
To give the maximum potential time before Foxy's next attack

Important note: When BB/TC are in the vent, you must keep the mask on until they leave (listen for the bangs in the vents, along with timing it well in the case of BB). If you take off the mask too early, they will stay and make you run out of time for Jack, if you take off the mask a second too late, Foxy will kill you. Timing is very important!
For clarity's sake, since I didn't specify, "you heard Mangler", means the static radio noise that Mangler makes in every camera he's in and when he's nearby.

Repeat


You can also vary the method slightly, and you can sweep to check both vents (left and right), to reduce the chance of specifically Toy Bonnie killing you (not sure by 100%, I heard that TB can stack behind Mangler)- however the timing for both Foxy and Jack is tight at all tights, and sometimes, it is impossible (nobody has a guaranteed method of beating 10/20 yet). There is more than one way to beat 10/20, this is just a guide.

Final note:
I recommend that if you do check for Toy Bonnie, be wary of how wound up the Music Box is. I personally don't like to check if the Music Box is less than 75% wound up, unless I haven't been attacked at least twice in a row. You can see that in the second completion video, I only check for Toy Bonnie when the music box is wound up a lot.


Updates:
As of 1.032, holding down the flashlight before putting on the mask no longer works. It shouldn't make much difference with Foxy, but it might for some people.

First of all, important note repeated: When BB/TC are in the vent, you must keep the mask on until they leave (and not a moment sooner or later!) (listen for the bangs in the vents, along with timing it well in the case of BB). If you take off the mask too early, they will stay and make you run out of time for Jack, if you take off the mask a second too late, Foxy will kill you. Timing is very important!

7 winds of the music box is roughly just enough to survive consecutive attacks if done quickly enough and shouldn't trigger Foxy, if other steps are done quickly enough. This will fail sometimes, when an animatronic pulls you off cams instantly when the music box is already wound down low. You can still survive this extra attack potentially twice, as long as you kept the music box wound up at all other times. 7 windups does not guarantee that Jack can't kill you on 10/20s so feel free to experiment.

Foxy will kill you if you don't flash regularly, however Foxy cannot kill you when you are being attacked and seems less likely to kill you if BB or TC is in the vent (this may be related to the timing and number of windups I used). The important thing is that Foxy should give you just enough time to take off the mask and flash everytime you are attacked (at least if everything is done quickly, in my experience). However, if you wait roughly a second (could be more or less) with the mask too long, on any attack, or on Balloon Boy or Toy Chica, then Foxy will kill you, and this should constitute the majority of Foxy deaths until you learn the exact timing and can also accurately gauge the timing for when BB and Toy Chica stop peeking out (for BB it's mostly non-random timing after you mask, for TC, it's semi-random).

All of the old animatronics and Toy Freddy will kill you if you don't mask on within less than a second.

Golden Freddy kills you if you flash him once in the Office, or for an indeterminate period in the hallway. He can kill you when other animatronics are blocking him (unknown if this is a glitch). If you mask first thing when dropping cams, and are conservative with flashing, you should be safe.

When Mangler arrives in the office, you will hear static on cam and louder static in the office. This is the queue to mask and wait for the noise to end. This often coincides with a Toy Bonnie attack.

Toy Chica has a roughly 50/50 chance of killing you if you go on cams in 10/20. This may be due to the saturation of attacks in that mode or simply because she's slower at attacking. Sometimes you will be in the position where you have to risk Toy Chica killing you to wind up Jack. Winding up Jack is generally more important than masking for Toy Chica when Jack is flashing orange/red or about to, since Jack's chances of killing you are practically 100% if left alone for very long when in the red. Again, sometimes you'll have to take risks in 10/20s, it's not guaranteed to win.

In my experience, if you ignore Toy Bonnie, and don't remask in the quiet parts unless you are sure he's about to attack, it prevents deaths that would've occured from Jack if you paid attention to Toy Bonnie (specifically when you get attacked consecutive times and then pulled instantly off camera- if you ignored TB, you survive, if you masked for TB, the time you lost not winding Jack has made Jack's music box low enough to kill you). However this is subjective conjecture, and sweeping the right vent light eliminates most of the threat from Toy Bonnie from a run- use either method.

Office shadow on video (right at the end)
https://www.youtube.com/watch?v=z4-q4Sh5n_s

Office shadow + extended reaction (longer version with theory & reaction, overtook the previous video with more view so I'll add the link for this one as well)
https://www.youtube.com/watch?v=4PGn6uVGJrs

If you want to share this guide with someone here is the link:
gtm.steamproxy.vip/sharedfiles/filedetails/?id=342233059