The very end of the chapter 25 disclaimer:
Though we find the characters of TBBT to resonate with us your fans. We also know it’s impossible to develop the full emotional, intellectual and range of these characters in 24 to 25 twenty minutes episodes per season shared between 7 characters. Therefore we endeavor to do that for you, making people happy, sad, laugh, cry, and angry about that development. Should we wish to actually profit from them we would change their names. This would be the adventures of Floyd and Edna rather that Leonard and Penny.
That’s the end of the disclaimer everything below here is a doodle.
It’s a rather simply concept, each show is about 22 minutes long, take out 2 minutes for titles, credits and fade in that leaves with 20 minutes.
Devide that by 7 and each character would get about 2.86 minutes per show. Realize the primary trio of the show is Leonard, Penny and Sheldon, give them a little more screen time say 4 minutes that leaves 8 minutes for the other 4 so 2 minutes a piece if you have no guest star appearances, mother, fathers, etc. With those constraints in mind you should have great respect for the writers who can put out TBBT.