First, you should go through the timers list (DVR*3) daily or when you add to the schedule to check which shows are to be skipped--you can also do this on the Sling interface. This is the only way you can be sure. The highest ranked timer WILL be given preference in every case I have seen.

The suggestion to change the default extension from 1 before and 3 after to say 1 before and 1 after is needed because with 3 or more minutes after, the show will be forced to override ANY following show--bumping it--although that should be a conflict subject to priority. You can use 0 min before on networks like HDNetMovies and HBO as they keep to the schedules. Broadcast networks and those with commercials are often early-to-start and late-to-finish on the moneymakers.

Occasionally, I have to delete a show and add it back to get the right tuner to be used despite being in single mode because it did not resolve the conflict on its own.
-Ken