What's the difference between SLR time-lapse photography and quick playback after normal shooting?

It should be time-lapse photography or interval photography, not time-lapse photography.

If the number of frames per second is the same, it is no different from the effect when the camera plays quickly.

But the former is frame loss during recording, and the latter is frame loss during playing. So the latter can choose to play normally, while the former has no choice but to play "fast forward" content. Of course, the former records smaller files than the latter, and the same storage space can store more content.