Cylinder? Whenever you want to, just keep your weapon clean.
Sideplate? Here's a story. About 25 years ago, a male friend gave my Mom a .38 special snubby S&W. I forgot about it. Last year, she moved, and as she flew out for the first trip, I'm holding the .38 until Christmas for her. It's been fired, probably 2-3 boxes a year, with little more than a thorough wipedown & bore clean thereafter. I decided to take down the pistol completely, including the sideplate. After research online to make sure I wouldn't run into anything I wasn't ready for, I took it down.
The internals of the pistol were absolutely immaculate. I gave it a very light spray of Rem Oil, laughed, and put it back together.