For what it is worth, I am a new victim of this problem. Drove off with my new REx one week ago and like so many others have TOU-2 meter to take advantage of much reduced rates after midnight. With my previous Leaf, it was a simple matter of telling the vehicle to start after midnight and finish by 5AM. I have a level 2 AV wall charger left over from the Leaf purchase which has performed flawlessly for 3.5 years, but has no intrinsic timer.
With the REx, I stumbled through the poorly written Owner's Manual--whose instructions do not fully correspond to the actual menus on the Control Display--and set a departure time of 5:30AM, figuring from my prior experience with the Leaf that level 2 charging of a fully drained battery normally took less than 4 hours. After this, I set the charging for "low cost" with parameters of 12:30A start and 4:45A finish.
In the last 2 days I had two long commutes requiring brief use of the range extender and thus a nearly fully drained battery. With the above settings in place, I put the charging cable in at about 7PM. The i3 began charging immediately (at rates about 30% higher than my intention), then shut itself off about 1.5 hrs later, leaving a "charging error" notice in red on my iRemote app. This AM I awoke at 5AM for an early commute, only to discover a 1/3 charged battery. Fortunately I did not have to depart for about 1.5 hrs and I managed to get the battery up to 80% charge, but again at an unfavorable rate (could be worse; rates from 12-6P go up 300%). And it forced me to use the range extender late in the day.
What otherwise defies me is that the Control Display says I am set for Level 1 charging, when there is no such selection (nor, contrary to the manual, a choice to pick Level 2). I wonder if the battery software thinks it is Level 1 and of course then starts charging well before my low cost time zone, since to accomplish a full charge by 4:45A it WOULD have to start more than 8 hrs before. The manual makes reference to a choice to use Level 2, but this is not available on the Control Display.
The business has repeated itself again tonight as I type. This is ridiculous--truly sheds a bad light on BMW. As does the delayed availability of the Smartcharge app.
Amateurs. Perhaps they need to talk to the Leaf development team.