Different agencies calculate their overtime periods differently, but all end up fairly close to each other.

I know some agencies that have a 0-minute grace period and others with a 59-minute grace period. With some, as soon as you pass the grace period, the grace period is ignored (i.e. 30 minutes is free, but 31-59 minutes rounds up to a one-hour charge, and 60-119 minutes is a two-hour charge), whereas with others, the grace period is factored in (i.e. on a one-hour grace period, minutes 60-119 are charged as one hour and 120-179 are counted as two hours).

Regardless, they all come out relatively close (an hour off, at most), and yes, they all do charge for a full day of optional products as soon as you're charged an hourly fee.

And hourly fees are usually one-third of the daily rate, so once you hit hour number three, you're basically fully into your next day's rental.

Most managers I've talked with will consider rounding down if you're close to the cutoff (especially if you passed the cutoff while waiting in line), but being well into your second hour by the time you pulled up into the lot means that you really have no right to expect any further grace beyond the grace you already got, and it's certainly not something to boycott a company over (especially given they all do the same thing). If they do, it's icing on the cake. (It always helps to be very polite and pleasant when asking for extra grace like this.)