I don't think it would really hinder creativity. But I do think the realities of TV production make it extremely low priority to do so. When they're rushing to get their show produced on time, on budget, the last thing they're going to worry about is how long it should take to get to Vulcan at warp 8 from Cardassia.
It may not have to be precise, but just having a general understanding of what is where might not be so bad.
Two weeks (if we're talking about TV and not movies, where ST:V failed hard) should be plenty of time to just realize what distances are not quite right. I'm going to use an example from Enterprise, since it is the clearest offender of establishing a law and then breaking it. In "Broken Bow", they say that Neptune and back in 6 minutes is roughly how fast the Enterprise is. Neptune is at its shortest, 4.3 billion km away, which would make a trip 8.6 billion km, or roughly one-thousandth of a light year. That would mean the speed was one-hundredth a light year per hour, or about 90 light years in a year. This actually wasn't too far off from the fan-described formula for TOS. But then they say that the Klingon homeworld is 4 days travel. Aside from the ridiculous political implications of that, in that amount of time, they should only be able to travel one light year, which isn't enough distance to even reach any star from here.
Now, of course this sounds nerdy and possibly over-analytical, but they have hired people who are science advisers, yet they make some pretty terrible mistakes. It doesn't seem too far fetched to me to just have a good portion of it established beforehand, and then to work from there. To me, it seems like a logical method of storytelling.