Different formats of the same film have different development times because of the agitation cycles and methods used to develop them. A roll of 120 film developed in a small tank will need one time because of the rather rough agitation caused by the inversion of the tank and the reels inside. The same 120 film will need a longer time if developed in a large tank because the agitation is much more gentle. Sheet film has another time because the sheets are shuffled once every minute or 30 seconds. It's agitation is also more gentle than small tank.

Different films need different times because of the emulsions used. The only way to get the same times using the same developer would be to use different dilutions. This seems like more work than it's worth. He should stick to one type of film.

Because of the small size of a 35mm negative, it seems to lose contrast when enlarged above 8x10. So grade 3 paper tends to be used more often as the standard when printing 11x14 or larger. You could just develop the film longer, but you risk blowing out your highlights.

I hope this answers your questions.

-Greg