Your tenants' expectations are perfectly reasonable. If contractors come to perform work that require them to access private areas, or that may be disruptive, I also expect advance warning. I mean, nobody wants to have the pool maintenance guy come in when the whole family is in the pool (nor does said maintenance guy want that to happen).
Whenever a contractor is supposed to come to my place, my landlord shoots me an email and confirms I'm ok with the schedule (or simply informs me if there is no choice). It's kind of basic courtesy.
If there's scheduling issues, I usually tell her to tell them to contact me and I work it out with them - no need for her to spend time going back and forth between the contractors and me in order to find a time that works for both of us. This has only ever happened for maintenance inside the home, though. If it's outside and I'm not required to interact with the guys, all I need to know is who's coming, when (approx.) and why. But I do expect to be informed in advance.
If it's not on private (enclosed) areas, like my front yard, I don't care. I usually don't know when the yard maintenance guys will come (neither does my LL, tbh), and I'm fine with that, because they don't have to get inside a fenced area.