I know I'm late to the party. But the kW-hr and Joules debate always pops up.
One more time on this: If one has a gallon of water, that's an amount.
If one pours out the water over fifteen seconds, then the rate that water is being removed is 0.25 Gallons/minute.
Energy works the same way. The amount of energy is in Joules. A kilogram of coal, when burned with oxygen (C+O2 -> C02 + heat), gives off energy; about 30x10^6 (30 MJ). A power plant pays $$ for a ton of coal, burns it to extract the heat energy, then converts the heat energy into electrical energy.
The rate that one converts or uses energy is, in SI units, Watts; and One Watt = a rate of One Joule per second. That 100 W lightbulb in the ceiling is, yes, using 100 Joules per second of energy, and that translates right back to the amount of coal (or whatever) the power company is buying to provide that energy. And, yeah, they buy coal in so-much-bucks-per-ton.
As others have mentioned, all of this makes a lot more sense if one plays with Joules, Watts, Megawatts, and/or Megajoules. But somewhere along the line power companies started charging for energy in units of kW-hours. So, yeah, around here, turn on ten 100 W lightbulbs, wait an hour, then flip the power company $0.15.
But it also shows up in battery sizes. You buy a Tesla, say it comes with a 75 kW-hr battery. That's how much energy it can store. Connect it to a 10 kW source, and, in theory, one can charge the car in (75 kW-hr)/(10 kW) = 7.5 hours. Connect it to a Supercharger that can do 250 kW and, if one didn't care about the health of the battery getting charged that fast at high levels of charge, one could charge the car in (75 kW-hr)/(250 kW) = 0.3 hr, or 18 minutes. (In reality, the rate of charge slows down above 30% state of charge or so, so it takes more like an hour or so to take a Tesla from dead empty to 100% full, but I digress.)
So, keep your units straight. You'll be happier, your calculator will be happier, and you'll stop annoying the pundits.
(There was a Tesla forum I used to be on where a particular troll used to mess up these units, on purpose, just to confuse newbies. Don't you be that troll.)
Finally: As regards the charging station. If you end up paying for the electricity, then don't bother, you can charge at home. It'll be more convenient since you won't have to keep on moving the car out of the charging stall so other people can get in. Very roughly, ye Bog Standard J1772 cheapie has 32A at 240V, for a charge rate of 7.68 kW. Your M3 gets around 0.25 kW-hr/mile (Notice! Units of Energy Per Mile!), so a 40 mile trip uses around 10 kW-hr of energy. Time to charge that amount would be 10 kW-hr/7.68 kW = 1.3 hours, at which point you'll have to leave your office, move the car, and let somebody else in. Which might be a bit of a pain on rainy days.
At home, if you've got a TWC hooked to 240 VAC and a 60A circuit, that charges at 45 MoCpH (Miles of Charge per Hour) at 11.52 kW. A round trip of 80 miles would use 20 kW-hr, so you're talking a little under two hours to get the car back to where it started. You gotta sleep sometime, so do it at home.
Alternatively: Say that work decides to provide the electricity for free. So, 80 miles a day -> 20 kW-hr; say you get charged $0.18/kW-hr, so that's $3.60 a day of electricity cost that you'd be avoiding. That might make it worth getting rained or snowed upon, your call. My son, who lives in California and has an M3, gets that perk and doesn't have a charger at his place for that reason.
At my place of work the company's put in a couple of Chargepoint stations that can deliver 28A at 208 VAC, but they charge $0.40 an hour to use it for employees. Others who happen upon the spot get charged $0.50/hour. The rate is 5.824 kW; so they're charging $0.40/hour * 1/(5.824 kW) = $0.0687/kW-hr. Which ain't bad. But I've got Home Solar, so my electric costs are near-zero, so, again, I don't bother.
Good luck!