Some days are good. The rest are a crap shoot. A few weeks ago I got 9 hares out of a 300m by 300m area in well under 2 hours. I went back a week later, spent the whole day there - still tons of fresh tracks everywhere - and only got 2 of them, both of which were so well-hidden under logs/brush that I was very lucky to have spotted them. I had to send my daughter down into a labyrinth of deadfall to retrieve one of them, it was in so deep.
It's just the way it goes. I consider myself a pretty experienced and capable hare hunter, but I can't claim that I have completely figured them out.
One thing I do use, with about 70% accuracy, is the solunar calendar. Sometimes it is just plain wrong, but more often it is a pretty good indicator.
Also, more often than not, sunny days are good.