1. In 8x18 (Freaks and Geeks), when Dean and Sam tell us that they met Victor "years ago" in Spokane, WA, on a rugaru hunt - they are really telling us that they met Victor AFTER September 2008, because they did not know what a rugaru was until episode 4x04. (This is where it REALLY helps to know the "Knowledge Timeline" of the Winchesters and not just the temporal timeline, which the writers are always f*cking with anyway.)
2. Also in 8x18, Krissy informs us that Josephine and Aidan were of great help after her father was killed, just after Josephine has told us that her family was killed "3 months ago"... which means that Lee Chambers was killed 3 months ago OR LESS. Now, I don't actually know when this episode takes place, but odds are it's around late march sometime, which means Lee Chambers would have been killed in December or Early January. Merry Christmas, Krissy.
3, 8x19 (Taxi Driver), takes place largely in Missouri - however, Dean has to travel to Maine at one point, which is approx. a 25 hour drive. If we DON'T assume that the Impala has magical powers, that means that Sam and Bobby spend approx. 48 hours in Purgatory AFTER their scheduled meeting with the reaper. Some of those hours (probably around 12, would be my guess) are spent before Benny even shows up.
4. Another interesting 8x19 Sam fact - if we take the sequence of scenes as a chronology, then it took Sam ~7 hours to find the rabbit hole between Purgatory and Hell. If we assume it would also take him 7 hours to get back tot he meeting point, that means that Sam spent 10 hours in Hell, both looking for and then escaping with Bobby.
5. By the end of 8x19 (assuming Sam and Dean didn't stop to sleep on their way back from Maine), Dean hasn't slept for 72 hours (assuming he doesn't sleep while he waits for Benny to show up), and, if Sam didn't sleep in the car, then he would have been awake for 108 hours (I'm assuming, though, that after 84 hours of no sleep, 72 of which were spent in Purgatory/Hell, Sam probably slept the whole way back to Garth's boat after he and Dean had that little chat about Benny. That being said, maybe one doesn't get tired in Purgatory or Hell).
Now, of course, take all the Purgatory/Hell time reasoning with a grain of salt. I'm measuring them here based on how much time is passing on earth - we don't actually know how time/space works in these locations; they seem to be fluid things that can change at whim.