Nah, can't fudge the start of the semester and mid-terms. Can't fudge on certain holidays either. And Buffy's birthday is a week AFTER the bracelet (Witch ends on Buffy's birthday Monday with the cheerleading trophy's eyes moving--the rest of the episode was the week before, so Xander's present just being friendship is fine). It's a scene where you could conceivably believe people aren't talking about her birthday and the characters could conceivably celebrate after school, because the subject is Amy and Catherine in one single scene. Teacher's Pet is likewise the week before mid-terms, except for the very last scene being on the Monday of the next week (and it's the same week as mid-terms on Wednesday-Thursday-Friday). Angel at the Bronze at the end is sometime over the weekend (Saturday or Sunday).
In one's birthday month, it's not at all uncommon to round up to using the age you're turning really, really soon. WttH and Witch are excusable with Joyce saying Buffy is a 16-year-old girl a couple weeks or a mere day early. The crescent moon thing matches the semester's beginning (bravo to whoever looked it up).
Once again, you're not realizing just how many days episodes take place across. Some episodes are only a day; some are more than a week! Some are continuous arcs that overlap days repeatedly (air dates become useless here). Every time there's a day/night and outfit change, it's usually a new day unless stated or by necessity (if an episode ends during a morning and you desperately need to double up when an episode starts at night, I've doubled them before with no other option). Some episodes outright tell you what day of the week it is. Episode scripts (not transcripts) also often give extra details that hint or even tell the day of the week or specify how much time has passed between scenes. Deleted scenes also give hints about how much time was intended to have passed (such as Joyce coming home from the hospital in 1x07 or Angel being the only attendee at Tina's funeral mid-episode).
Then there are things like Spike watching Dawson's Creek (now there's an air date that matters, because it's specifically stated--that season didn't start until October!) or the Vikings game (look up their 1999 sports schedule) playing in City of... Yes, I'm the dork that even looked up what nights the Vikings were playing in 1999. It happened to work flawlessly, including with the crossover, but made it very clear what day of the week that scene occurred on.
I looked up several California schools to compare schedules and looked up differences in holidays between counties. The only time I had to fudge was the fact that Torrance HS celebrates both Washington's Birthday/Presidents' Day (3-day weekend) and Lincoln's Birthday (the week before). Well, episodes are majorly in trouble in season 2 because of Valentine's Day and Oz's werewolf schedule if Lincoln's Birthday on Monday is observed. However, then I found out that other schools even in the same district (LAUSD) and in other districts (Sunnydale is based on Santa Barbara's map) don't even get that day off like Torrance HS does.
7-3-0's countdown actually starts in May (May 17, 1999 if May 16, 2001 is when she died), whereas school ends towards the latter part of June (June 23 would be Graduation Day 1999). The countdown had already started a bit, but Faith's words are still in the spirit of a two-year countdown. Dawn is having Parent-Teacher Day in Bargaining (which suggests she's been back to school for a few weeks) right before Buffy is resurrected, so Buffy definitely died around May 16 and was resurrected around October 10 (147 days).
Cordy's birthday being stated to be May 22, 1981 means that everything after Birthday happens AFTER that date. The rest of the season with the Angel-Wesley-Holtz-Connor stuff is mainly in June. Connor was probably conceived on the night of February 23-24, 2001 (note that Nathan Reed's computer calendar fills in the date for Dead End and random W&H things in March-April). Connor was born the night of November 29-30, 2001, given the stated full moon the night after. Connor was in Quor'toth about 18.5 days.
Joyce died right after Spring Break (April 23, 2001, most likely), as I Was Made to Love You specifically takes place during Spring Break (Warren left the Aprilbot behind in his dorm for the week and that's what the party is celebrating).
