That's pretty much what I do, only more so. I have a setback thermostat
upstairs that is set to 90 between 9 am and 9 pm, and 73 between 9pm
and 9am. I find that this works well, as the long cool down cycle
really dehumidifies the upstairs, it really doesn't do it at once,
since the thermostat is a "smart" one and it calculates how well it did
at achieving its goal and adjusts the next days attempt to start
earlier or later. The downstairs one I completely shut off at night and
manually start in the morning. We are home all day, so it isn't exactly
your scenario, but I see no real reason to keep them all that close in
temperature, a little cold or hot probably transfers between the two,
but it isn't all that noticeable, and I can't see how it could
adversely effect the equipment.