I used to record Enterprise on videotape.
No ads, no opening or closing credits = 39 minutes.
This was important, so that I could fit four episodes of enterprise and a 30 minute sitcom (minus ads, minus credits) on a 3 hour tape, which i could not do with DS9 or tng, without cutting off the tail end of the sitcom.
Episode 1 of Discovery was 42 minutes 51 seconds (including cbs all access logo, opening credits and ending credits.)
Episode 2 of Discovery was 40 minutes 33 seconds (including cbs all access logo, opening credits, season one preview trailer and ending credits.) and it's possible that in future times that they may add a "previously on Discovery" catch up reminder for the terrestrial broadcast.