[lkbm]

I recall it changing when Star Trek: Voyager was on the air -- at least for Voyager.

Looking at Amazon Prime, seems the episode length changed from 46 minutes to 44 minutes going from Season 5 (1999) to Season 6 (2000).

(What I was remembering was 47 to 45, but this is a vague memory of a Usenet post I read twenty years ago.)

EDIT: Also, I should note that Voyager was on Fox. If you're talking about NBC specifically, I have no data.

[olyjohn]

Voyager was on UPN. Maybe in some areas where there was no UPN station, the local Fox station picked it up.

[lkbm]

Ah, you're right. I forgot UPN even existed. Thanks.

[pwinnski]

Good point, it's likely different for different networks.