Hopscotch achievement takes place in 8th level "Ruin Rush" after the first jumping sequence there will be a path to the right. You have to keep it open by elevating red block 2 or 3 times. Low gravity pick up will drop and you'll be able to jump over the 3 highest pillars to small line of blocks at the left wall. After picking up the time pickup you'll get the achievement.

Whatever Floats Your Boat takes place in 9th level "Hover Headway". To get this you'll have to complete jumping sequences between the green checkered bars at the end of platforms without touching the ground.

Both achievements are part of the solutions to beat Dev's times.