It may depend on the type of inserts you are trying. Some of the more rigid orthotics take a little longer to adjust to. Some patients start by wearing them for a few hours at a time and build up over a few weeks to full-time wear.
If they are custom made, you may need some minor adjustments during the early period of wear. It's a good idea to get the fit just right before resuming all activities. Likewise, runners need to ease back into their training schedule over a few days to weeks.
With patellofemoral syndrome, pain occurs behind the kneecap with certain activities. It's always a good idea to avoid repetitive deep knee bends and squatting. These activities often make the pain worse. Once you've had the orthotics for a month to six weeks, you'll have a better idea how much more you can do without flaring up the knee symptoms.