Many composers are concerned about their output rate and feel intimidated by hearing that composer x wrote the score for feature film y in just a few weeks or something like that. However this whole issue shouldn’t be bothering you too much. The more experience you have the quicker you will be in composing. Many things will switch from “let me try if that works” to “I know this will work”.
So if you’re just starting out and still learning, don’t worry too much about speed, you will get quicker at that automatically. It is also safe to say that without making quality compromises, writing a mean of two to three minutes of music a day is still a pretty good reference point. That still includes days where you just get about 30 seconds of a complex action sequence done.
Considering speed rates of composers on blockbusters with supposedly incredible short amounts of time to write the music, you should be aware that ghostwriting or “additional music” is in such cases quite common. The main composer usually is taking more of a supervising role and writing thematic ideas while there are more people to flesh out things. They are sometimes credited, often uncredited. So the bottom line is to not be too concerned about your general output rates as long as you can hit your deadlines.