I feel like it really depends upon your relationship with your dealer.
If it's strictly business, then call whenever; if you are in the habit of calling at 1am and your dealer goes for the sale, that's up to him. If he's like, no, it's too late, then you can either be flexible personally, or find a dealer who is on your schedule.
If you guys are buds anyway, there's a totally different level of respect. You know his schedule and have to respect it as part of a friendship.