The length of time the controller will remain in Float after battery voltage has dropped below the Float Voltage setpoint. Typically, this is the result of insufficient solar charge, heavy loads on the battery, or a combination of both.  Keep mind, it’s common for heavy load to draw battery voltage down below the Float voltage for brief periods of time. Depending on the type of load used, this could happen multiple times during the Float stage.  However, the Float Exit timer is a cumulative timer.  If the total combined time below Float voltage exceeds the Float Exit timer value, the controller will exit Float and resume the Bulk/Absorption charge stages as necessary.