Greenside,
You are making me sit down and analyze my activity. OK, not a bad thing to do once in a while!
I can't answer the question as to why I am more successful in the later mornings and not in the early AM(??) All I know is that I am confident in my statistics.
As for "mid-day" calling I have a few "rules" that I swear by and will continue to do so. I always try to set up so as NOT to make the critter have to cross long stretches of open ground. They just won't do it. So, the alternative is to set up along side of cover, keeping as much visibility as possible down the tree line, sage line or whatever. Sometimes the coyotes simply step out to see what's making the sound. Keep a sharp eye out for these situations. Binos really help!
The other rule that seems to hold for true for me is that I cannot call a yote TOWARDS a road of any kind. Why? This one is easy to answer. They know "trouble" passes along these roads and won't commit to approaching them.
The Howling part of your question is most interesting. On a trip to Alberta with "Redfrog", I noticed he howled all day long and we got results. (This is where the joke started about "never howl at noon.") Wrong. It seems to work there and works in Central Oregon as well. (High desert country)
My theory is that even though we don't hear howling very often in the mid day time frame, the coyotes will at least take notice of this activity and might get curious. (I must add here that I was a LOUSY howler, so I practiced as much as possible to get better. (That translates into practicing only when the wife was out of the house!! But you all know that story!)
Anyhow, the better I got at howling, the more dogs I had come in, even in mid day. (Thanks Jim R.)
As for evening calling, I usually am too pooped to do it, so I am not the one to ask. (I have never called at night, though it's legal in Oregon on private land)
Now, with all that said, I am still not 100% pleased with my success rate. I may go 10-15 stands over a few days with no "hits". But when it works, I am more than satisfied and am convinced Oregon yotes "sleep in!)
Shoot straight and often,
Rustydog