The switchover between an expiring on-body medicament delivery device and a replacement on-body medicament is made to eliminate or significantly decrease the time where an on-body medicament delivery device is operational to deliver medicament to a user. The replacement on-body medicament device is attached to the user and prepped for operation while the expiring on-body medicament delivery device is still operational. The switchover between on-body sensors also may be improved. Methods for calibrating a replacement on-body sensor while the expiring on-body sensor is still operative are provided. The calibrating may be performed quickly so that there is no gap in operation between expiration of the expiring on-body sensor and full operation of the replacement on-body sensor.