A simple method I have used with unknown film/developer combinations is a variation of a drop test.
Take a length of film from your spool. (typically the leader or a few inches behind that)
Get a vial of your developer and lower a small section of the strip into the developer. Each minute or two, lower again. The idea is to get stripes with increasing development times on them. Keep a note of your times.
Then once your first section has been in the developer "long enough", take the strip out, wash it and fix it.
Then inspect the strip in front of a strong light source. Identify the darkest section just before totally black and that's your time.
This is just to get a ballpark time, of course. Once you have developed a test roll, make your usual adjustments.