For me, getting it done in the morning when my kids were in bed used to be the only way. Otherwise they'd bother the hell out of me until I'd give up mid-way through a workout. But I came to accept the reality that I am simply not a morning person, and facing that unattractive truth forced me to find another time that I could stick to. Right now I'm working out during my lunchhour. Sounds crazy, but it works great. It keeps me out of the faculty room listening to people complain, and I eat less since I have to munch at my desk. It's a pain to shower again midway through the day, but there are no excuses. (And I'm working out with the volleyball, basketball, and football coaches who don't let me skip! Ever.)
If morning isn't working, be honest with yourself and find another time that is. No excuses.
"The grass ain't greener, the wine ain't sweeter, either side of the hill" The Grateful Dead