In Season 6 episode "Entropy" Buffy has a conversation with Dawn that goes like this:
Dawn: "No, you're not, it's not that, it's just... what if, instead of you hanging out with me? Maybe I could hang out with you... Why don't I come patrolling with you tonight?"
Buffy: "Oh. And then? Maybe we can invite over some strangers and ask them to feed you candy."
Dawn: "Well, you guys went out patrolling every night when you were my age."
Buffy: "True... but technically, you're one-and-a-half."
Buffy: "See, I thought a little levity might... but okay, also no."
One and a half, would yes, then mean start of season 5. Around October, which was the time the episode "Real Me" came out.