It's my understanding that the charging rate adjustment only works with the 120vac device delivered with the vehicle in the USA, not when connected to a 240vac device. That may change per market. It's there in case that receptacle you plug the thing into may be on a shared circuit with something else to help prevent from overloading the circuit. Say, it's plugged into the same circuit as your garage door opener...might work fine until you tried to open or close that door, or maybe use a saw, compressor, vacuum, or some other tool. It won't overload the EVSE, as the EVSE reports to the car the maximum it can deliver and the car adjusts itself to that, but potentially not if it was a shared circuit.
In the USA, the maximum EVSE charging rate is 7.4Kw. Power depends on the voltage supplied, so with the same EVSE device at a 208vac commercial input would provide less power than a 240vac line you may have in your home (power=volts*amps). Since the pilot signal from the EVSE announces how many amps, and not power it can provide, a 30A device at 208vac won't max the i3 out, but in my case, my 30A EVSE at my typical 247vac does.
The time slot for charging could be a little easier than the way they implemented it. It isn't all that clear. It also can be misleading, since, if you plug the car in while the charge is below a certain point, it will start to charge a bit, then stop and wait so that the battery doesn't sit at a low charge level when it could get cold and become damaged.
Last, the car does calculate, given the available data based on the pilot signal from the EVSE and its current state of charge when it will be finished charging nor does it actually show the current charging rate in amps or watts.
For less than about $30, I wired in a meter to monitor the power, voltage, and amps my EVSE was pulling. It's operational power is in the 20W range when activated (lights and contactor and logic), and maybe 3W when not (indicator lights and logic).
While I have the CCS input on mine, I've never actually plugged it into one. Probably should have before the warranty expired, but never found the need as I use it as a local runabout, as it was designed for, not a road car on longer trips so I'm always home to plug it in without intermediate charging along the way.
Keep in mind that the car does slow the charging rate down, regardless of the capacity of the EVSE or CCS unit you plug into as the batteries approach full charge. That's one reason why they rate the CCS charging times to 80% rather than 100%, as after that point, the heat buildup and charging rate come into play in trying to preserve the battery health. Level 2 charging, from what I understand, gets to a higher level before it starts to taper off partly because that slower rate (7.4Kw versus 50Kw rates) between level 2 and CCS differ. With an EVSE, it can get somewhere in the 90's percent range before it slows down. Also note that not all CCS units out there will max out the i3, either. While there are now some capable of up to 350Kw, the car won't use more than the 50Kw rate from it, and BMW offered some price leader 25Kw CCS units to dealers to soften the blow about installing them that you might see around. A DC power supply that big is somewhat expensive, and requires some major power line upgrades to be able to install.
2011 535i x-drive GT, 2014 i3 BEV