It is configurable by you (from within DigiGuide Marker configuration for the DABDigR marker) but it is defaulted to 10 minutes.
If, when you add the marker, you are inside the interval then it is actioned almost immediately.
(note - the way that DABDig handles this is different for each device - but for GBPVR in particular ... as soon as DABDig is called it will attempt to put the entry into the GBPVR schedule (slight exception if the start time has already been reached))
Paul WebsterDABDig creator