Holy fuck, you really want to challenge yourself as an artist? Only give yourself 30 minutes. You never know how much you will surprise yourself. I never knew I was capable of drawing so fast.

There is a simple trick I learnt to aid with this: never get hung up on the details, block out the big shapes first. I technically finished this sketch in 18 minutes, but by not getting hung up on detail I was able to use the remaining 12 minutes to polish and detail.