Ten Forward seems to be open around the clock and you can always create food with the replicators too. And we see the officers work in shifts. So I assume “breakfast” is the meal before your shift starts and “dinner” is after it is over. Other than that, there is probably no “meal time” as such.

We mostly follow the bridge crew around the captain but presumably there is a whole other crew of officers for the “night” shift. (In fact, there is an episode when Troi has the helm for that shift.)