Not sure if it's a time travel. AU, or not, but, I know there is a watchers journal, from the past, and when they read it, I am sure Buffy and Spike go to that time, again, it has been a while, so, acn only really remember that main part, the slayer at the time of journal thinks Buffy and Spike are bad at first, til they explain, sure there's a watcher too, wish I could remember more, not sure what season either, anyone? x

I think you are after this fic...
Things Present – Things Past by Estepheia and Marcee
Two timelines. Two Slayers. One problem! How does Buffy get back to her present time when she's sucked into the body of a Slayer in 1880? Can another Scooby who tries to rescue her survive the past? Plus, meet William and witness Spike's big decision!

Thanks, I come across that the other day, am sure Spike and Buffy were together, there was exerts from a watchers journal, not sure if it was the same watcher, or through the years or wat?, sure there was another girl, watcher, So frustrating, that I can't be more specific, whether it was a spell, time travel, or what xx

Hi,
Is it 400 Days by PassionFish?
Buffy and Spike get thrown into another dimension...or is it?

http://dark-solace.org/elysian/viewstory.php?sid=1099&ageconsent=ok&warning=5

Hi Girlie, I don't think so, driving me mad x

Grasping at straws here - they don't travel back in time (that I remember) but there are a lot of watchers journal entries that you might be remembering? ---

The Prophecy by Witchiepoo - Summary: AU fiction that takes place post-Normal Again. Buffy and Spike are having a baby. How did this happen? And what does an ancient prophecy, a French Slayer, and New Orleans have to do with this? Join Buffy and Spike as they struggle to bring their child in the world. They will need unconditional love and a belief in each other to survive.
http://www.dark-solace.org/elysian/viewstory.php?sid=867

EDITED: Now that I've remembered more of this, I wish I could delete this post. Definitely not the droids you're looking for.

Don't think it's any of those, was a while ago when I read it, ugh x

Well - glad you could not delete your suggestion - The Prophecy sounds like a story I would love to read.