How much air loss over time is considered normal / acceptable for a hybrid tire? I'm looking for a rule of thumb as to how much air loss over time is considered acceptable / normal for a hybrid tire.

Surprisingly I have not been able to find much on this upon Googling.  In this post:

How long should a road tyre hold its pressure?

Two people with road bike tires in the 110-120 psi range stated they normally lost 5-10 psi per day.  This seems high, especially if closer to the 10 psi figure.

In my particular case, I'm running 700x32mm tires and the sidewall states "Min 35 psi, Max 75 psi".  I'm currently inflating every other day to about 75 psi (perhaps slightly higher, but always under 80 psi) and I find I'm loosing about 1-2 psi per day, which seems roughly normal but I'm really not sure.

I'm using Giant tubes I got from a Giant dealer so I'm confident I'm not using poor quality tubes, and the tires are Giant branded hybrid or "gravel grinders" that are relatively tough and in good shape so I'm confident I don't have a puncture or slow leak problem (wheels/tires/tubes all OEM/stock parts on a 2017 Giant AnyRoad CoMax).

How much is considered normal?
Tyres will always lose pressure over time, I would say that for cycle tyres 1-2 psi is closer to the norm for most including me. This is mainly due to the microscopic pores in the tyre/tube which air molecules escape through over time. 

However don't forget that the air in tyres also expands and contracts with temperature, so on colder days tyre pressures will decrease slightly, and vice-versa on warmer days pressures will increase, it is considered that roughly 1-2 psi with every 10 degree increase/decrease in temperature is the norm here. 

Natural deflation also occurs more rapidly the higher the pressure so as you reach a tyres max pressure it will deflate quicker, and thus to keep your tyres at max pressure you'll need to inflate them every couple of days due to the higher pressure loss rate.