Dragon 65 features Lewis Pulsipher's Timelord NPC class; I've written extensive additions and changes to that class, since one of my brothers played one as a PC. They're an excellent option for introducing time travel in general into your games (GH or generic).
On the GH front, Lendor and Cyndor both manage/represent the time portfolios, so having them espouse more modern concepts of time like sundials, having specific hours in the day and night, etc. seems like a general approach that would work well for introducing different ideas about time into the campaign. Higher level clerics may also have access to time gates, the ability to summon time elementals (details in Dragon 69, and in one of the newer 3e MMs), etc.
I'll also second the suggestion of artifacts, in particular the stranger techo-like artifacts like the Machine of Lum the Mad, the Mighty Servant of Luek-O, and such.