so just re-read the hobgoblin arc and it mentions that it has been 9 months since the first issue, so altogether i would say there has been a total of about a year and 3 months since the beginning of ultimate spider-man.
Again, take any time references in USM with a grain of salt. Bendis' time-jumps in the previous issues: 3 months between the first arc and the Double Trouble arc, 4 months during the Hollywood arc, 2 months during the Carnage arc, and I think there might've been a few other mentions of time-jumps or how long had passed between certain events. So, 3+4+2=9. So if we're to believe thats accurate, the events of the previous issues had to happen in less than a month for all that time to pass and Bendis' time-jumps to remain accurate. It just doesn't work.
And its not a case of certain time jumps occuring between or during earlier issues, since continuity wise there's always a reason this can't be done. For instance, Gwen appearing towards the end of the Hollywood arc (before and after the 4 month time jump) means the entire arc HAS to occur before the next arc (the Carnage arc), and since she lives with Peter during this arc, it occurs after the Public Scrutiny arc (if I recall thats when her dad, Capt. Stacy was killed, and she moved in with Peter and Aunt May).
As I've stated many times, Bendis is extremely liberal in his timeline references (in both mentions of time passing and continuity--for the Ultimate line in general and his own USM tales), so never set them in concrete or try to structure the other Ultimate titles around it. I use the time references in Ultimates and Ultimate FF mostly, since those seem to be the most accurate overall.
Remember, if you figure Bendis is to be believed that 9 months passed between issue #1 and #72 of USM, then by this point in the series Peter should have been Spider-Man for well over a year. But, we know a year hasn't passed, technically, since Peter is still a sophomore, and all his friends are still sophomores, there's been no summer vacation, etc.
Bendis himself has said he never wants Ultimate Peter Parker to age...in his opinion the regular Spider-Man got boring or lost something when Peter grew up, went to college, became an adult, etc. Bendis wants to keep Ultimate Peter/Spider-Man 15 years old forever. Seriously, I remember him saying exactly that in interviews several times. So, while time seems to progress in other Ultimate titles, it doesn't really in USM, which makes for strange bed-fellows continuity-wise when those other titles
do progress in time. I mean, if two or three years has passed in the Ultimates (since their creation), and approximately three to four years for the UFF (since their creation), how has only one passed in the USM title (when its referenced events in other titles which span those time frames)?
Its not a big deal, but for continuity nuts like myself it can be mighty irksome.