Bre I should have put some comment about the 1440, didn't think to. Also the fact that the 'hh:mm' restricts the time to hours and minutes.
And, of course, if anyone wasnts to work out the cost/second the time format would need to be 'hh:mm:ss' (so now you've got seconds as well) and the multiplication would need to be (pause to use calculator) '*86400'.
(And if you want it per day, leave off the '*1440').