The time it takes for your science officer to receive back the scanning pulse is...
You can't have any
sort of starship TV adventures with STL sensors. It just won't work.
The distinction you seem to desire is clearly not between STL and FTL sensors, it's between insanely fast FTL and ridiculously fast FTL. And that
distinction, while dramatically possibly quite significant (say, giving Kirk time to grab that sandwich), is in absolutely no way related to "forethought" or "pre-establishing". In all situations, the plot dictates whether Kirk be eating sandwich or barely having time to blink; the facts will wrap themselves around that necessity.
If the background and scenery matters at all, it needs to be set it stone first and not shifted around all the time for writers' convenience.
That isn't so even in historical fiction: if drama so requires, it is always possible to insert a faster than usual horse messenger, a ship that bravely sails during the winter under unusual calm, a mercenary who fights on credit for an unusually long while, or a castle that wasn't really quite
there. The background becomes the more
interesting when its dramatic role gets highlighted by an exception. Or when it gets deliberately exaggerated and stretched, such as every incident in a Wild West town being decided on the intervention of the local cavalry when the show is about the cavalry.