I was helping out a friend back end of last year to get some new builds done before christmas on a labour only basis. Only 8 houses.
He had previously worked for a large contractor who do a lot of the new build developments around here before going solo.
They typically would first fix a standard 3 bed house in 4 days. Second fix and testing for certification taking another 2 or 3 depending on spec.
They didnt see point in rushing normally because they were usually on a price per house rate depending on size, and there was always a week allocated for the electricians in the schedule, so they could take upto 5 days for first fix before the other trades got held up. they had another 3 or 4 allocated for the 2nd fix. So always had capacity for slight over runs
With some builders they plan out the job poorly and things are always being moved around. it often shows in the final finish of things like skirting and decoration within the property as the customer doesnt see the wiring.