Why would it be only for middle/end game ?
(Your mod is pretty much mandatory, right from the start, with some of the more complex mods, like AngelBob and Pyanodon...)
Anyway, it's not so much about what the default should be, it's about the issue that changing that setting doesn't seem to have any effect ?
An example of another player having an issue with it here :
https://www.youtube.com/watch?v=fqWaqaOAxnI&t=19m59s
(Before that he has spent a good 5 minutes adding recipes, and resetting all the Factories he stumbled on to the starting ones.)
And later you can see that this setting had no effect !
https://www.youtube.com/watch?v=fqWaqaOAxnI&t=34m37s
P.S.: I like how you put "base time" in a dropdown, saves on precious space !