I've been wondering about similar things. I was thinking about how neat it would be to use short bits of film for testing cameras/lenses as well as exposure/development. But for the latter, I think that development would be different from a whole roll because a) hardly any chemical change in the developer and b) the movement of liquid with the same agitation would be different in a mostly empty tank.
But as your goal isn't transferring results to whole rolls, I'd say start the experiments with a bit shorter dev time than you would for a whole roll, maybe 10-20% less.
If you really want to develop just one frame at a time, you could try to do it in a film canister in the dark, in that case the ratio of developer/film surface might be similar to normal roll in tank, so normal time? Just be sure to leave some air in it for agitation.