How much time can I ask for between joining a new job as a software developer in the Bay Area? My RSUs will vest by April 15th and should I be upfront and tell my new employer that? I would have to ask for 2 months if the offer is made on Feb 15th.
You can ask as much as you like, but how much the company is willing to wait depends on the company size and situation.
If you're joining a giant company like Google or Facebook as a generic software developer and haven't been assigned to a particular project, the answer is probably "quite long", and two months is likely fine. A friend of mine at Google asked for, and received, almost a year off before he started -- although he was hit by a sudden family crisis near the end of the interview process and moving to a new country for the job, so this is definitely at the extreme end of the scale.
But if you're joining a small company that needs somebody to fix the frobnicator so it stops discombobulating the widgets right now, they're unlikely to be able to wait even two weeks. This would hopefully have been made clear at the interview stage though.
The other alternative is to use your stock vesting as leverage when it's offer negotiation time: if they can offer you a sufficiently large signup bonus to make up for the loss, you don't need to wait two months, and everybody wins!
Having been in this situation before, I can say that it is best to just tell the new employer your situation: that you have RSU's that vest on a particular date and that you can't announce you're leaving before that date. Most people will understanding because these RSU's can be significant.
8 weeks is a lot but not an unreasonable amount of time for really good candidates in hard-to-fill positions. It is possible to negotiate that if you are careful.
Whatever you do, don't announce your departure to your current employer before you vest or you risk losing the RSU's.
Asking for two months may very well be a deal breaker.
Also keep in mind the wait may be even longer. Read the documentation and realize they could terminate your employment the moment you give two weeks notice. That could leave you short by two weeks. Therefore you might have to wait until April 16th to give your notice to protect yourself.
I have heard of several weeks delay to get past a vacation or a planned business trip with the old company. Or a few weeks to get past an anniversary point for vesting.
If the new company is trying to fill a void or to meet a contractual obligation a several months delay can cost them money. They could also be nervous that you are still looking for a better job, and may never show up.