I think it's ideal to have some sort of part time job. In my case, I have a full time job and can't leave it for two reasons:

1) I am on H1b-Visa [More Important than #2, so didn't even think about applying for YC this summer, though I would love to]

2) I need $$$ :-)

I typically try to wake up early(6am), hit the gym, put in my 8/9 hrs at work so I am free by 5-6 pm. Now I have potentially 6 more hours till 12:00 am during which I try to get some work done on my personal projects OR go to silicon valley meetups etc Or just laze/party out completely some days. [Potentially 30 hrs in 5 days]

So, time is not really a problem, it's more of a Time management and Motivation that will carry you forward. I am still tweaking both :-)

PS: On another note, I will be up in the SF city for StartupWeekend. Still looking for people to partner up ? Anyone Interested ??