for the multi engine rating you tend to fly about an hour a day. can probably do 2 hours a day, but remember that all that asym work will be tough going on yer legs.
for the IR, you can look to fly about 2 hours a day. if you're going part time, it will probably require a little bit of refreshing each session to relearn the previous lesson, so don't be upset if you take a little longer than the 50 hours minimum. good weather sees it done in 5 weeks full time, 13 weeks if done sat and sundays.
IMHO, full time is the only way to go, but i understand that people have other commitments and this may not be possible.