Can be done on many different stages. Got my trophy personally on the first stage if day 6.
Heavy blocks = Grey blocks
You must move THE SAME BLOCK 10 times.
Personally, at the start of stage 6-1, you start with 2 heavy blocks in front of you and your standing on a floor of 4 regular blocks.
Just pull out the heavy block and slide it back and forth 10 times.
I actually died at the beginning of stage 6 about 8 moves in. The game auto rewinded before i died and i was able to move the block the last few times.