The buffer could be based on a base amount (assuming these are done at the store location) same as it is currently.. but also add an additional amount of time based on the driving distance from store location to the address of the new appointment.. basic Google maps API, get the estimated driving time from them and boom you have custom buffers that include the prep time AND drive time.. because you don't know if the drive is ten minutes or an hour.. This function alone has made schedulers not practical for many home services niches who are still relying on secretaries to book meeting times to allow for drive time