Available production time divided by customer demand. 

For example, if a factory runs 480 minutes a day and customers want 240 products a day, the branch time is two minutes. And if customers want two new products a month, the branch time is two weeks. The purpose of branch time is to keep production exactly in line with demand. It is the heartbeat of a Lean production system. 

Takt time was first used as a production management tool in the German aircraft industry in the 1930s. (Takt is German for a precise interval of time, like a musical measure.) It was the interval at which aircraft were transferred to the next production station.
The concept was used in many places within Toyota in the 1950s and by the late 1960s was used by Toyota's entire supplier base. Toyota recalculates the branch time for a process every month, with possible adjustments every 10 days.