In case you are still looking...
Lost in Time by Spikeskat
Set during Halloween. Buffy and the gang "turn into" their Halloween costumes. But, before Giles can break the spell, Ethan does something that has a profound effect on Buffy... and Spike is along for the ride. 65 Chapters. Completed. --All pages link from each other fine, including the epilogue if you click from the bottom of Chapter 65.
other Lost in Time verse fics...
A Heart Whose Love is InnocentRenee's story. 4 Chapters. There was also For Love of a Wolf: Alric's story but I don't have a working link for that.
Phoenix Rising: Clayton's Story I only have a link to the prologue so it may have stayed a WIP.