Aside from a few years ago when DST was changed in the US, the airlines all know when times change and build flight plans knowing what time it is.

If you just asked why is a flight at 11 am on saturday and noon on sunday then it'd be a DST issue.

My flights to/from PHX are 1 time for part of the year and another time for the other part since AZ doesn't change for DST and is MST all year.