The only info I could find was from Wikipedia, which did not cite their source, but states that two years pass between the events of Spider-Man (2002) and Spider-Man 2 (2004). No passage is stated for the time between Spider-Man 2 (2004) and Spider-Man 3 (2007) but it feels like less time than passed between 1 and 2.
Spider-Man 2 takes place two years after the events of Spider Man. Peter has left Midtown High and is in his first year at Empire State University.
Granted, he knew he had responsibilities. He had learned that lesson all too cruelly when, two years ago, he had stepped aside and allowed a thief to escape from the scene of a robbery. He had done so in a fit of pique and with a sense of poetic justice: The thief had stolen from a wrestling promoter who had screwed Peter himself over money owed him. As the thief had fled, the promoter shouted in Peter’s face, livid over his lack of action. Peter had said with the sort of smug confidence that comes with being truly self-righteous, “I missed the part where that’s my problem.”
Spider-Man 3 takes place a few months after Spider-Man 2. He's finished his first year of university and is right at the start of his second year. During the summer break he appears to have done some PR work and dramatically improved his image with the City which is why it probably feels like more time has passed.
Everything that Peter had done in the past two years to atone for his great sin was simply an endless pursuit in the face of an existence that had suddenly become terribly, even blindingly unfair.
Peter, seething with barely contained rage, said between clenched teeth, “I don’t think you’re doing your job. I watched my uncle die, and we went after the wrong man. And now you’re saying”—his voice began to rise in pitch and volume—“you had suspicions for two years? Witnesses? Why weren’t we told about that?”