Scrapes occur where they do because of the overhanging limb. The overhanging limb is used as a communication device all year round, but the scrape underneath is only used around the rut. All deer of both sexes use the overhanging limb, but usually it as an older buck that is the first to open a traditional scrape. However, once open, every buck will rework/reopen the scrape. What I find interesting is (when mature bucks are present), the older a buck is, the more likely he goes through the full sequence of working the overhanging limb, reworking the scrape, and then urinating in it. The youngest bucks are the least likely to go through the whole sequence.
As for when bucks work scrapes, most is at night, but there is a slight peak in activity right around first and last light. I also find it interesting that in a good acorn year, the morning peak (lasting into daylight) is greater than the evening peak, but in a poor acorn year the pattern is reversed - the evening peak just before dark is higher than the morning peak. There is still an evening peak of scrape-working in a good acorn year, but it tends to occur the first hour after dark, while in a poor acorn year that peak occurs in the last hour of daylight.
Another strange thing I've noticed since I began monitoring scrapes with video cameras and can see deer full behavior, through most of the fall does only work the over-hanging limb at a scrape. They pay little attention to the scrape on the ground. However, like flipping a switch, suddenly every doe becomes VERY fascinated with the ground scrape, often spending minutes sniffing it, and this sudden change in behavior occurs about 5 days before breeding explodes.