A lot depends on how long it has been since you started a new one, started a child this age or the age mix of the group you have. That determines what you need to change - if the new baby is going to mean changing outside time so baby can nap or making the big kids play with lego only in a certain space and changing their normal routine it will take a lot longer than if the place is already set up for babies and it just means adding one more highchair to the kitchen and allowing 5 more minutes at diaper change time.

Any change takes a couple weeks to work out most of the kinks and then you can start to work on making the routine normal. This all hinges too on how well the child transitions to the group - screamers don't ever allow you to get back into a routine till they get over it.