At -30C, 5min per hour for your block heater is a joke. It might help a little, and if it were free, then yeah, whatever. But having to pay the kind of parking rates that people that buy parking in downtown office buildings do? Nope, that's just a rip off.
What would be better is if the plug ins came on for an hour from 4:00 to 5:00. But that would cost more, as now the plugs are on for five minutes an hour from 9:00am to 3:00pm, so a grand total of 25 minutes a day. My wife rarely leaves before 5:00, so for at least the last two hours she's there, her car gets no power to the block heater.