I have a pied female, Aster, she's about 3-4 months of age... I got her on Christmas Eve from a pet store I usually go to (the pet store handles their animals, etc., it's an awesome place).

She hasn't had any source of belly heat since I took her in, as I am low on funds, etc.
I was able to feed her on 12/27/15 easily even though she hasn't been warm at all, she had a mouse hopper from Petco (they don't have rat fuzzies).
She's also currently in a 10 gallon tank for the time being, she's been crawling all over my girlfriend and doing so has warmed Aster up a bit.

Diablo, 6 years old, is fasting but has a UTH on. He's in a 30-40 gallon tank himself.

I was planning on building a rack system soon, hence why she's in a 10 gallon tank.

My questions are:
1. Should I remove Diablo's UTH and put it on Aster's? Would Diablo be okay?
2. Would Aster be okay without a heat source?
3. How long does it take a 3-4 month old to poop?