what are the shifts like?  

If I may put my $0.02 in, based on 14 years with Rocky Mountain/Air Methods:

Are they 12 hours on and 12 hours off, 7 days on, 7 days off, 2 shifts per day to cover 24 hours?

I'm retired some 4 years ago, but at that time my base schedule (a 'community based program') was 3 days 8am to 8pm and 4 shifts 8pm to 8am. That results in 8 calendar days on duty even though it is nominally a 7&7. A matching number of bases in my program did 4 days and 3 nights. The original idea was that bases would switch from 4/3 top 3/4 but that never happened. Everybody got used to their existing schedule.

I heard some places (not sure who) only fly day times.

I am told that that was so, but my experience was that that applied only to select bases. Perhaps existing hiospital contracts did not allow night flights and/or community based that could not hire sufficient pilots to cover 24/7.