I let fry stay with the parents until around an inch, unless they start to cannibalize before that.
I let haitiensus fry stay with the parents a little too long in one case years ago, and they ate gaping holes in the male.
As Duane noted, the fry will actually injure the fins and scales of their parents in some cases. This is especially true of discus whose fry feed from the parents' slime coat.
I usually remove mine as soon as they go free-swimming, but in a community tank set up I try to siphon them as soon as they hatch into wrigglers. In extreme cases I will pull a whole slate/rock and hatch the eggs in a separate tank, but usually the parents do a good enough job that they can at least guard them until hatching.
For Jag the breeding cycle between 4~7 weeks, so it's better to keep fries with parent around 4 weeks then move them out. My experienced on my Jag that all the fries safe for at least 5 weeks before the parent wipe them out and get ready for new spawn!
I've had my last batch of grammodes in with the parents for 2.5 months. They ate the eggs of a new spawn about 2 weeks ago which is great because I'm up to my eye balls in grammodes fry/grow outs.