(1) Measure time against itself. Time thus passes at the trivial rate of one second per second.
(2) Measure time against a non-temporal standard:
If I tell you that Bikila is running at the rate of twelve miles per hour of the pure passage of time, for example, then I have also told you that the pure passage of time is flowing at the rate of one hour for every twelve miles run by Bikila.
(3) Claim that the question involves a category error. Perhaps rate talk essentially "involves a comparison between some normal change and the pure passage of time." (p.843) The pure passage of time itself then has no rate to speak of. But it passes all the same.
These responses all seem woefully inadequate. Especially the third - what does it mean to speak of movement that occurs at no rate? Surely this is just to say that it doesn't literally move after all. The second seems similarly senseless: to move just is to move through time, i.e. to be in different positions at different times. And the first says nothing of substance.
Things that flow may speed up or slow down. Not only does movement entail a rate of movement (contra 3), but it must be possible for this rate to change. If time passes, it must be possible for God to alter its rate of passage - to 'fast forward', 'rewind', or 'pause' the flow of history. But that is incoherent. So time does not pass.
Why is it incoherent? Well, suppose God decides to pause the flow of time for five minutes. How much time has passed? None, for time is frozen. But ex hypothesi five minutes have passed, so time is not frozen. This is a contradiction. (Similarly for the other manipulations, which all involving changing the rate of time's passage to something other than 1 second per second.)