Jlc, welcome. I see you have been a member for a while, but just haven't posted much. Hopefully this forum will keep your interest. Be sure to share your experiences.
As to your coyotes coming in at irregular times and different days, well, that's the story here too. It is indeed difficult to hunt them when that happens.
The last coyote I shot was September 24. Since that time, a coyote has visited only twice, then it's off and gone until the next time, whenever that might be. I have to stay at the cabin (which is about one mile from my home) in order to hunt. When a coyote hits the bait, I try my best to hunt the following night, but I can't always due to family matters or weather. When a coyote pulls a one-night-stand, it's really difficult to hunt it.
I have put out leftovers - cooked meat, chicken scraps etc, but haven't noticed any difference in what a coyote gets first. Actually, I have put out cut up deer scraps along with cooked meat and can't tell any difference. Who know, maybe your coyotes prefer their meals cooked. LOL.
The Driveway alarm is about the only way you will be successful at a bait site. It's impossible to stay up all night and continuously be looking for a coyote. Best thing is to get some rest and let the alarm do the work for you.
Good luck. Keep us posted, along with good photos of course.