The time for boosting depends on the input power supply voltage. The booster circuit itself has been configured to boost to ~21VDC (so even if the booster is turned on indefinitely it won’t go past 21V). The higher the input power supply voltage, the faster it is to reach that limit. With 7.5VDC input (the default), it probably will take 500ms to 750ms. You can leave the boost time to 1000ms if you want to make sure it reaches the maximum.