I use gelatin. But I don't use it til I get to the keg. I know some people who keg will use it in the secondary and rack off the gunk (but I've heard gelatin works better when the beer is cold). But I usually just do a primary, then rack into a keg, put the keg in the fridge to cool it down, then add the gelatin. 4-5 days later, I pour a pint or 2 off and the rest is running crystal clear, then I carbonate. Some may say I can carbonate while the gelatin does its thing, but I've got my way and it works.
If you bottle I'm nt sure when to do it. Not sure if the gelatin pulls out any needed yeast to carbonate the bottles. So someone else may be of better assistance. Though I would tell you to wait and add the gelatin after fermentation is complete, bc things will keep churning and you'll probably need to do so again.