The early hours are by far the best to mow hay because the grass is wet, heavier and softer. Because of that, the grass provides less resistance to the blade and is easier to cut.
From the human point of view, the early morning is cooler, the scyther is rested and the cut grass has the rest of the day to dry.
Ideally, in order to not waste precious morning time, the scyther should prepare the blade the day before and have ready all the equipment needed for at least 6 hours of mowing. That includes honing stone, stone holder, peening kit (anvil and hammer), shims or a piece of leather to adjust the angle of the blade to the snath or to secure the blade if it becomes loose.
It is important to observe whether the grass is standing straight or lying down towards one direction. If the latter, we want to cut from the back of the stems—in other words, we are mowing in the same direction that the stems are bended. It is very difficult to mow the grass when the stems are pointing toward the mower.