Do i need to record all development process to prove that it's made in 3 hours? Can i still start?

yea you can still start and its optional but it would be nice, atleast i will

You don't, some do for their own head space, but it's an honor system here with a massive amount of skill sets and levels of diversity. 

 You can absolutely still enter and I can't wait to try your submission, the three hours is just to qualify for prizes