This can be a problem, but not an insurmountable one. The most important thing to do is talk to your would-be mentoring organization(s) and let them know about your schedule constraints. Given the length of the community bonding period, it is possible for you to do some upfront work to get yourself prepared to power through your project with a bit less time, but your mentor must be bought into this plan *and* you will still need to get some code written weekly, even if it is much less than you would like.
HTH,
LH
PS- For those who don't know it, HTH = hope this helps. If you are having trouble understanding all those acronyms in open source, like RTFM or AFAIK or AFAICT or IIRC, etc., try a web search first. If that fails you, there's always the acronym dictionary:
http://www.acronymfinder.com