I'm a PM'er also, but not as late as some of the other posts. I generally work out as soon as my 18-month old daughter takes her nap, usually around 2 pm. I get my 5 year old settled in with a snack, drink and something to do/watch and off I go. I work part time and on the days I work, I'll work out later if DH is agreeable, but I try to use those as rest days. Years ago, before kids and when I had more energy, I was a regular evening exerciser and I always really enjoyed it.
I've made several attempts to work out early morning and for whatever reason, it's never worked. First of all, I am not a morning person, and while I don't mind doing weight work early, I absolutely cannot jump around and do any sort of aerobics. It makes me want to puke! Also, it's inevitable that the earlier I get up, the earlier my kids seem to wake up, too...must be kiddie radar! Whenever I mention to my husband that I'm thinking of getting up with him (5 am) to do Cathe, he just laughs...he knows it'll never happen!