Dark fantasy series I read in the 90s

[jchase]

Hi everyone! I'm trying to recall the name of a dark fantasy series I read as a teen in the 90s, but I'm pretty sure the books had been around a while at that point. The protagonist in the first book was a male child, and I have very vivid recollections in that book of his being chased by a dark figure on a horse. I recall some sort of time-travel like elements, and at one point he escapes through a hidden door in a fireplace I think. I really thought the series title had the word "Dark" in it, and I feel like "Time" might have also been in there somewhere, maybe as a title word in the book but not the series, but I've been unable to find anything in my google searches. Any suggestions of titles to consider would be appreciated!