Ilford recommends 2-5 minutes in fresh Rapid Fix (Ammonium Thiosulfate) at 1+4. I always use fresh fixer and have never needed longer than Ilford's 5 minutes with any film, including TMax and Delta. Shorter times could probably be used for non-tabular films. Best to do a clearing test with your particular film and then fix for 2-3 times the clearing time.

Some reminders for those less experienced:

1. Mix the working solution thoroughly. People sometimes neglect good mixing when dealing with liquid concentrates. There is an Ilford tip sheet which warns that the liquid Rapid Fix concentrate needs to be thoroughly stirred into the water to mix properly.

2. Proper agitation. I would recommend agitating for at least 10 seconds per 30 seconds throughout the fixing time.

Ralph and Sly are both right. It depends on the various dyes in the film, and the film base itself may have a slight tint. For example after fixing and a complete/thorough wash TMax 100 is virtually colourless, while some Ilford films such as Delta 100 (in 35mm at least) will have a very slight bluish cast.