You can also use an EVSE like a JuiceBox Pro or other connected EVSE's to charge to a preset limit. In my country most jurisdictions also offer a rebate on them.
As I understand it, you can charge for a preset number of hours, but the EVSE has no communication with the car about state of charge. That means you still have to do the arithmetic to get the correct SOC.
I believe you are correct, you still have to do the math AFA how long you have to charge at a given amperage to get to a desired SOC%.
It's easy on my 24kWh 6.6kwh equipped charger Leaf using L2. If I have a 13a L2 output EVSE I gain roughly 13%/hr, bump it up to 16a and I charge at roughly 16%/hr, 24a=24%/hr and finally the max 30a(27.5a) gets me close to 30%/hr. Of course charging rate can vary by extreme cold temps or what SOC% your currently at(charging rate slows down near the top of SOC, above 90s) but where most people would charge, 10-90%, I figure roughly for each amp of L2 I gain a %/hr charging, 120v charging is roughly half those numbers.
The voltage of your L2 can also change things a bit, 208v vs 240v, with 208v giving you slightly less %/hr. Most N. American homes being 240v and commercial or industrial buildings(work or non-single family larger dwellings) being 208v L2.
Personally I don't screw around as much trying to stop at a particular % SOC anymore, I just time my charging so it only reaches 100% right before I leave for work or an easier way to stop charging at <100% is to use the charging timer in your car and tell it your leaving for work a couple hours after when you actually plan on leaving. I guess once summer comes and I can stop using the power hungry heater so much I can go back to 80% but for now even a full 100% charge only shows ~60 miles on my GOM
in the summer I get the same 60 miles with a 80% charge, ya winter kills my range!