Astrologian conceptually is most similar to Warren and Orran Durai from the Ogre Battle series and Final Fantasy Tactics. Their jobs are, respectively, Astromancer and Astrologer. Astral Stasis, Orran's signature attack, is even in FFXIV as a unique limit break.
In FFXIV, Astrologian is a field of study in-game with magical properties that is based on time and space interactions.

If you look closely at the astrologists in Coerthas Central Highlands, they are in fact wearing the traditional Time Mage garb. Astrologians being an evolution of that paints a pretty clear picture, and if not consider the original translations for some of their ability names.
In the Japanese version, Stella is Don't Move, Disable is (was) Don't Act, and Swiftcast (while not unique to Astrologian) is Quick. When including Time Dilation and Lightspeed, and their space themed abilities (Time Mage was always, always in Final Fantasy implied to be proficient in Time AND Space magic) Gravity, Combust, Malefic, (one could argue Celestial Opposition), you can see that Astrologians are primarily classic Time Mages with Warren's cards and the nocturnal/diurnal healing system unique to FFXIV.
I wouldn't mind an offensive/support caster true Time Mage class too, but the evidence is pretty damning that Astrologian is what we've got.

Geomancer on the other hand is much trickier...the Astrologian quests paint them as a unique separate job altogether, but it's not known how much they and Astrologian overlap.