We are a pre revenue early-stage mobile app startup
Depends on the accelerator, but generally speaking within 30 days of the application period closing. Response times/ranges however are typically defined in the details of the application, thats been my experience.
In terms of helping your chances, thats relative and depends on a number of factors. Referrals from alum and/or mentors are always helpful. However, being a 'pre revenue' early stage startup, traction + revenue never hurts :-)
Hope that helps. Let me know if you'd like to chat further.