definitly mon-fri, but the support crew is located across the globe, and depending on which Dynatrace product you need support for - this will vary (due to timezones..etc).
Also depending on what kind of issue you need assistance with. If its an actual bug (I've found several) - fixes can go from as short as a couple of days to several months. (my personal experience with appmon, dcrum and synthetic).
I've had many supporters i could simply call up or Skype/lync/webex with, but naturally they have to triage the ticket first.