for lasers not built into the frame, how often do you need to recalibrate the aim?
Good lasers will hold Zero, no problem. Off hand I can't remember a good laser not holding Zero.
My primary HD laser/light is the Streamlight TLR-2.
When I'm shooting the pistol during the day I remove the Streamlight to keep it clean. Sticking out front of the barrel like that the lens and light case get pretty cruddy.
And when I'm using a bipod on the AR the laser is in the way, so I remove it.
When I replace the Streamlights the lasers are still dead on.
When I first install a laser I sight it in before shooting by just getting and holding a good iron sight, sight picture on a target 20-25 yards away. Then I adjust the laser dot so it appears to be sitting on the front sight as I hold the proper sight picture.
Or if the gun has a Red Dot installed, it's very easy to sight in the laser, I adjust the laser dot to the Red Dot
After shooting and fine tuning the laser I take note of where the laser dot is in relation to a good iron sight, sight picture. (or the Red Dot)
This way, at any time, without firing a shot I can check to see that the laser is still Zeroed.