Looking at the world from your own two year olds eyes you might also want to disrupt their life as little as possible which means not a great deal of time off or your child will go from being entertained by all their friends and a set routine to just "hanging around" while everyone rushes to do baby things or sits to rest and does nothing - not fun for a toddler and that is more likely to lead to issues for them. You said hubby would be there and mil part of the time.

Only you can decide really how much time you think you need. Is it possible that you will have less ppd issues if there are more things needing your attention or does all the demands from extra people make it worse? That may for sure influence your decision.

Anything more than a couple weeks to a month and expect children to get used to their new temporary daycare and plan to stay there instead of returning. Which is another option - to actually close when your baby is born and then when you are feeling better and got the new routine set you can advertise and start again.