DVR start and stop times off

all recordings are starting early and ending early. in order to get the complete show the recording we have to extend the recordings by 3 minutes. This has been happening for over 7 months.  two techs have come out got a new box and still have the issue. Done the chat multiple times.  Still no fix. The additional 3 sometimes causes shows not to be recorded.  If we want to record 4 shows in one time slot and there is a show recording in the previous time we only get 3.