I have mid-morning planning this semester. My favorite is planning over the period that has lunch. It's nice because it splits the day, and because that period is the only one that NEVER gets tampered with! Whether we have pep rallies, assemblies, early dismissals or late starts, lunch-period planning is never cut.
This planning period used to be my least favorite. Early planning gives you a chance to ease into the day, and to review your lesson plans and feel completely prepared. Late-afternoon planning helps you get prepared for the next day. Mid-morning is just kind of bleh. It's not early enough to be helpful for THAT day, but it feels too early to be getting ready for the next day when you've still got several classes for THIS one.
However, I also have the last lunch period. And I'm finding that mid-morning planning and late lunch break up my day nicely into small, more-easily-manageable chunks. We're also required to stay for an hour after students are dismissed, so I have an end-of-day breather as well.
All in all, it's been a pleasant surprise to find out that what I thought was going to be a crappy schedule is one I very much enjoy! :)