I am plannign everything about my game right now. But i dont know if i can create the base in 3 hours. If i take 10 minutes more to create the last bit of art i need to make it look good, should i  take them, or is 3 h a hard limit

3 hours isn’t a hard limit (I think), just be honest that it took you over 3 hours when you upload your project.

And remember that you're doing it for yourself! So if you work on games regularly, the skill you'll acquire will be far more valuable!