I've checked other questions but none cover the topic of past contributions. I'm wondering how much weight does time spent before incorporating matter.
Do Founder A earlier contributions have enough weight to change the ownership split?
Is a 50/50 situation stable enough for decision making in the long term considering there are clear roles & responsibilities?
Joel Spolsky goes through a plan along these lines in great detail here:
Forming a new software startup, how do I allocate ownership fairly? As long as it doesn't cause resentment, 50/50 could work with some points you need to remember:
Most likely the accelerator has a lawyer or three on staff to advise on these exact issues.