Out of ten gigs my band might know the exact show time at maybe two of them. This would surely be true for a lot of artists, especially on a level where there are no actual organized tours.
It would be great if one could chose an option that says something like "To be announced" or "Check with the venue" instead of us having to guess a time. One would choose a time that´s too early as listing one that´s too late might cause unwanted problems. It´s not so good either, though, when you here people saying: - But you were supposed to start at 7! (and the gig turns out to be at 11!)