Overtime is a technology researched at a level 7 Town Center or above. Each time Overtime is researched, the time to assign laborers to a building (farm, refinery, university, or foundry - NOT lumber camps) is decreased. Overtime also decreases the time it takes to remove laborers from a building. Overtime does not stack with itself (so level 2 Overtime will give purely a 20% decrease in assigning time).

Link to the Overtime in the Database