I think first of all it might be a good idea to change the way you are thinking about it - instead of 'I don't have time', maybe it's a matter of 'I am not prioritising exercise at the moment' - I know it sounds a bit naff, but really we all have the same amount of hours in the day, and there will be people here with little ones, or full time jobs, or both, who find time.
First thing in the morning is my favourite time to work out, but when my boys were small, I would do it when they were sleeping during the day. And I walked everywhere, with a double buggy (it's just over a mile into the nearest town).
I do pretty much all my exercise at home - I have dumb bells, and lots of DVDs.
Start by fitting in one session a week, and work up to more.