Can I use some code parts from my other game project?  I already have some mechanics that also want to use in jam bounds.

And there is no practical sense to recode them from zero, but I don't want to cheat, so ask. 

It's simple mechanics like a time system or transitions for choices.

 If it's not allowed, what should I do?

Oh and also can I start drawing sprites, writing draft, and looking for backgrounds with music before February

Without making an actual build of course.