Except in Voyager (where due to the nature of the premise they had to be _somewhat_ consistent) this was entirely plot-driven. It could be anything from "real-t

Except in Voyager (where due to the nature of the premise they had to be _somewhat_ consistent) this was entirely plot-driven. It could be anything from "real-time comms halfway across the galaxy" to "we'll get a reply next week" to "no contact at all". Occasionally this even varied within the same episode.