When I am ready to do my HVAC tune up and check up the few times of year that I have them done, I always call the heating and air conditioning company in advance.
Usually a month in advance to schedule my turn up and check up of the central heat and a/c unit.
The reason I do this is to guarantee that I will be able to get HVAC home services from the local heat and a/c company. When you call only a few days to a week out, what happens is you take the risk of them not being available or booked up and it could be weeks before they can get a heating and air conditioning specialist out to your home to do the heat and a/c tune up. They do not treat it like heating and cooling repair. So I have found that calling a month in advance is the best way to go. I called this month just a few days ago to schedule my HVAC tune up and check up for this time next month, which is the beginning of the summer time months. And it is going to be a hot one this year. So I want to make sure that my central heating and air conditioning system is all up to date and working properly to avoid any kind of heat and a/c breakdowns in the middle of a heatwave. I had that happen to me once and it was not fun.