I sooo love time travel stories (even though it hurts my brain sometimes trying to sort them out) and the premise behind yours was great. I love young Snape just on principle alone, but when you toss a similarly-aged Harry into the picture, too... well, it's magic (no pun intended). They are even more perfectly suited as seventeen-year-olds. I love an insecure but commanding Snape, a charming and slightly clueless Harry peppered in with mystery, romance, intrigue and humor, and your story had them all. The Dumble Door was also very clever, but next time don't let Albus pick Harry's name! ;-)
Above all else, what enraptured me the most was the notion of Harry getting to live "both" lives. I loved what he wrote on the rose petal for Snape, the fact that he stayed (he stayed!!), their thrice-daily sex (which reminds me, I want to know more about the one where Harry was hanging upside down from his ankles *smirk*), and the scene right near the end where Snape comes barging into Dumbledore's room and is just so visibly heart-broken at the fact Harry is leaving. That really got me at the moment, seeing him so vulnerable and in love, but once I learned Harry didn't actually leave, it was even more poignant. Oh... *squishes Harry and Severus* ...so lovely. I'm glad they both get the lives they deserve!