I've used this method for years,with good results.
Assume you have 3 emulsions :A ; needs 14min, B : needs 12min ,C:needs 8 min.
Prepare chemistry for 3 films.
Load 3 reels and put B & C films in a spare tank.
Start process with film A.
At minute 2, add film B.
At minute 6 , add film C.
By minute 14 you will have 3 films correctly developed,and they can all be stopped and fixed together.
Obviously you need a darkroom to use this method..