They need fresh air all the time for sure.
I wasn't running outtakes for the whole room at night but room was big enough for them to use 6 hours whats in there in vegging stage. I was leaving only two slow passive intakes in the cabinet during the night for temperature purposes. Since i went to flower i switched to run lights at night, so they get dark in daytime, this helps on temps a lot. Switched all the fans with full speed and didn't effect on temperature at all. Plus helped with keeping dark periods humidity under control.
Hope this experience of mine helps.