One known type of bearing induction heater, described in EP0143091A1, heats the bearing to the extent desired by suitably determining the duration of the heating phase.  This document also describes a phase for demagnetising the bearing immediately following induction heating. 
Another type of bearing induction heater heats the bearing until a desired measured temperature of the bearing is reached. 
The desired heating time and/or temperature for a particular bearing is generally determined empirically and presented to the user of the induction heater in the form of a reference table. 
Induction heating times are of the order of 3-4 minutes for small rolling bearings and 20-30 minutes or more for larger bearings.  Decreasing the heating time required for a particular bearing is highly desirable.  However, whilst increasing the induction power of the heater would reduce the heating time, care must be taken to avoid locking or damaging the bearing due to the inner ring heating and thus expanding more quickly than the outer ring.