From the classical FF job system, theres just one mage type missing in this game, and that is actually the Time Mage, or also known as term of Chronomancer
Their Beginner Class/Guild would be Arithmetician and the location with be kind of shared with that of the Summoner in Linsa Lominsa in that place, where that of Summoners is underground and the arithmeticdian Guild would just be placed in the upper level of that place.
However, the quest that changes the place so that this new guild will be found there, can be played only, if you own Shadowbringers.
http://finalfantasy.wikia.com/wiki/Time_Mage_(Tactics)
Chronomancers would be for me Tanks in FF1, because this game is missing so far a magical based Tank. With the other two being physical ones, a Chronomancer would work differently.
Class Mechanic: Time Distortions
A Chronomancer can create up to 3 Time Distortions. When they create a time distortion, every enemy that gets affected by it, will be put under "Stop" effect and won't be able to move or attack automatically. Against bosses and other enemies immune to Stop will cause Time Distortions just heavy aggressivity towards the Chronomancer and blinds them, so that their attacks miss. Enemies of any sort get also slowed from beign affected by a Time Distortion so that their skills are used slower, giving players that way more time to react accordingly or to defeat stuff, before they can do something.
Whenever a new Time Distortion gets placed, the oldest one gets removed.
A Time Distortion is created when a Chronomancer uses the ground target skill "Timespace Rift"
Class Weapon: Greatshield (OH) & Magic Gauntlets (MH & OH)/shares Skins with Monk Fist Weapons
Greatshields are longer or larger Shields than normal ones that paladions are using, they are more defensive and therefore are the counterpart in the lesser defense of the other gear from a Chronomancer, that is no heavy plate armor stuff.
The defense of a Chronomancer comes lesser from gear, but much more so from their Spells and basically their gameplay concept of preventing damage, before it even happens, or in case somethign has happened, reverting received damage through manipulating timelines to a point, where the damage hasn't happened yet, essentially turning time back. This makes basically Chronomancers also a kind of Tank/Healer hybrid in the same way, how Redmages are kind of a DPS/Healer hybrid class