I have a blender project with 4 separate scenes which get combined in the compositor. Three of them are quite simple and mostly finished, while I am still working on the main one. However, every time I hit F12 or press the render active scene button it re-renders all 4 scenes, which is a waste of time. Additionally, each scene must be rendered at a different frame, which for some reason I seem to have to re-tell it every time I render, which makes having to render every scene every time an even bigger pain. So is there a way that I can just render one scene?
Does the scene you are currently rendering have compositor nodes? If so: rendering that scene requires it to render all the compositor inputs. You can deactivate the compositing step by unchecking the Compositing checkbox in the Scene > Post Processing properties.
You might also consider creating an entirely separate scene for the compositing, then render the other 4 scenes to stills. Use the stills as input to the compositor instead of scenes. This might speed up the workflow as you are tuning the compositing.