Disregard what you read in-game about that mask. The information given are wrong

Have you heard of geometric progression ?

If the answer is NO, then go read a math book for years 14 and +.
If the answer is YES,then you are good to go (and you understand why a 1.5% loan can require you to pay 200% in interest)

The Bandana mask works simply by multipliying the current amount of money you are carrying by a fixed value at a fixed time interval.

Currently the multiplier is x1.05 (AKA the common ratio)
Currently the time interval is 10 seconds (but more on that later)

This means that if you carry $1000 and wear the bandana mask for 1 minutes (=60 seconds = 6 time interval) you will earn this amount of money (in theory):

time = 0s -> $1000
time = 10s -> $1050
time = 20s -> $1103
time = 30s -> $1158
time = 40s -> $1216
time = 50s -> $1277
time = 60s -> $1341

Those are example values. The game round up to the next multiple of $100. So the example above would end up at $1600 after 60s.

There is a drawback to the money multiplication. This mask drains your health.
It's a mask mostly viable on a sniper (they can heal with their supply crate) or on a team where you have someone wearing the Cupcake Mask (best mask in game) and spawning donuts (heal +50 HP) or even have a gym bag near you.

The Bandana mask stops working if the wearer is a 1HP and will work again once the user heals.

The mask draining 1% HP per second, you know that without sustain you'll only have 1 minute and 39 seconds of efficiency for the Bandana mask.

But, there is a super secret. You don't have to wear the mask all the time for it to work. You just have to be wearing it when the client/server checks for interests ! This means, that for a 10 seconds interval, you'll only have to wear it for 1 seconds.
And by timing it perfectly, you can only consume 6HP per minutes and hold for 16 minutes and 30 seconds without sustain.

The time check usually occurs when the seconds of the remaining time (displayed on top of your screen) is a multiple of 10. But if the total time set by the server owner is not a multiple of 10 seconds (eg : 307 seconds for 05m07s), then the time check doesn't occur at the same moments, but still at the same interval.

Every minute, you gain 34% bonus. This a multiplicative. So after 2 minutes you gain 80%, after 3 minutes you gain 140% etc. The longer it lasts, the better.