Not sure that was ever the case... 5,000 on two shifts were each 10 hours a day, but I think they were 6 days a week. That's 120 production hours a week. On a 3 shift schedule, the number of employees on the 3rd shift might not be the same on the 3rd shift. As it stands, the Tesla Master Plan has 2 shifts with the day shift at 2,980 employees and the night shift is 2,030 employees. (illustration with 6,000 employees). Taken from their 2016 Master Plan as presented to the City of Fremont. In a 3 shift schedule, I am not sure the number of employee hours goes up all that much per car.
In any case, Model 3 production is very different from S/X where the GA is almost all human labor. So the extra employee count and production hours don't really divide in as cleanly.