I'm wondering this too. Poor DD has been constipated on and off since starting solids. We gave her prunes yesterday and this morning. I'm really hoping she goes today!
Depends on how much you give. We give half a container daily to keep DS regular, if he's backed up he gets the whole container and will usually go within a few hours.
Re: How long does it take prunes to work?
This for us too. Be prepared though, because it REALLY works.
BFP/Labor/Everything Buddy: Papetvet/Erpetdoc