PTO pay calculation: How does it work?

I could use some advice here. I’m getting ready to head back to work after maternity leave, and my plan is to burn through both my old and new vacation days right away. To bump up my average salary for future calculations, I’m thinking about moving the kids' dependents from my husband over to me. Is it smarter to pull the trigger on that now, or should I wait until I see my first paycheck after working a month without using any PTO? Basically, does tax get calculated on my salary while I'm on vacation? I heard they base the calculation on an average of the last three paychecks, but since I was
out on maternity leave, they just use the base salary from my contract.

Crunching the numbers.