I have some "solarised" (Sabat(t)ier effect) negatives in which the images look better reversed, so duplicating to film in this manner might be a way to get a good printable negative. Can anyone suggest a very general rule of thumb for starting times? Given the same light source, how do the exposure times for, say, 100 ASA film compare to those for a typical paper?

There are a lot of variables, of course; I understand that. I'm just looking for some guidance as to whether to start testing exposures at five seconds or two minutes!