I haven't seen one yet this year. But over the past several years, I have seen them from about 09:00 am to 04:00 pm or 5:00 pm. There are a couple of trees close to me that I have caught several swarms in. I got one out of it around lunch and just before dark there were two swarms in it. All three were good size swarms.
If you are talking about your own hives, once you see a hive swarm you will remember it. It looks like all the bees are like making a tornado, swirling around and in a little they are gone to a tree, bush or where ever. They will stay there from a few minutes to a day or so.
I saw a hive swarming, they stopped in a small tree, I went to get hood and box to put them in, and as I was headed over to them they were gone. Tried to see where to but after a few hundred yards, lost sight of them.