I always get the impression that Sin attacking Zanarkand is day 1, Tidus waking up in Spira is day 2, being found by the Al Bhed and going on a salvage is day 3, waking up in Besaid is day 4, leaving on the pilgrimage is day 5, I have no idea how many days it takes the boat to get to Kilika but it appears to be one day, so they arrive in the evening and perform the sending... therefore heading the Kilika Temple and fighting the Sinspawn is day 6. The ship to Luca appears to be an overnight trip, so the Blitzball tournament is day 7. Then they head down through Mi'hen, apparently on the same day, and operation Mi'hen closes day 7. On day 8 they head towards... well I can't remember much the sequence of the game after that as I only played it twice and have watched a fair few people at least play as far as that :P But it seems they take about a week to reach Djose at least.

As for how many hours or days pass for things like being teleported to the desert, finding Yuna in Bevelle with the airship, time spent on remand prior to the trial, time spent in a cage before being dumped in the Via Purifico, and time spent sitting around recounting the story before entering Zanarkand, spreading the word to have the entire world sing the Customer Services Hold Music of the Fayth... well those are kinda vague. I can't see the game's events taking more than a month because my impression of every RPG I've ever played is that somebody suddenly has their world rocked and suddenly has a duty to rise up and deal with it and abruptly discover their inner bad-ass, but RPG timescales are always a bit tough to gauge.