First of all, let’s keep in mind that a mythological role/ classpect/ God Tier is all about how you affect reality. Also, even with the same God Tier, certain outcomes of the classpect (most likely psychological ones) may differ from person to person.
How I understand Mages: Mages are most probably an active, knowing class, pairing with the Seer. One of the main differences might be that mages gain knowledge directly from (aspect) while seers gain knowledge through (aspect). Sollux knew things directly from the voices of the imminently deceased (THE DOOMED) but Terezi knows things through the outcomes of the actions she or the others take. (To be a bit more clear: a Mage of Mind, such as me, would have some sort of telepathy since I gain knowledge from aspect, and a Seer of Doom would probably see which actions may lead to a doomed timeline.) Seers are canonically said and proved to guide with their knowledge, and I think Mages may also have some guidance attribute, since Sollux at least tried to coordinate the sgrub session which ended up with the destruction of their planet or guided the trolls away from their doom by piloting the meteor, though I’m not sure about this one. Mages do seem to have some sort of complicated or conflictive relationship with their aspect: Sollux has successfully avoided death, but that has caused him a lot of personal distress, and Meulin doesn’t have a matesprit and is also currently being manipulated by her former one, though she doesn’t know and doesn’t seem heartbroken. Also, I think Mages use their knowledge to create their aspect. Sollux created sgrub and the moubius-double-reach-around virus, which killed all the Lusii thanks to his knowledge on programing, which is related to Doom because codes and rules are DOOMED things, and Meulin is a talented matchmaker.
How I understand Heart: I’m going to let bladekindeyewear explain this:
"Heart represents the soul, desire, affinity, ideals, and most importantly individual uniqueness. Certain inward inclinations, preferences, personality and ideals are built in to a person’s very soul. (The connections with love are obvious given the above, as they concern an individual’s attraction to another and the seeking of one’s “soulmate”.) Whether separated by sleep, by diverging experiences, or even by the nigh-impassable barriers between universes and universal instances, Heart guarantees that different instances of the same person share a core. A core which holds those facets of oneself most important to oneself, like both kid!Dave’s and adult!Dave’s creation of “Sweet Bro and Hella Jeff” on either side of Universe B’s scratch. People carve these core inclinations into the course of reality’s progression, shaping how it unfolds; as an aspect, Heart is how one’s individual uniqueness impacts the world around them."
How I understand Time: Well, Time is one of the fabrics of paradox space, counterpart of Space, and it seems to relate to destruction and, ergo, death or erosion, which sorta makes it similar to Doom, but that’s just because death is inevitable to anything alive and so is destruction to anything created. A time and a space player are needed for a successful session.
Mage of Heart: (such as Meulin Leijon) A fully realized Mage of Heart is probably a really empathic person who knows the mood, the feelings, the individual uniqueness or maybe even the intentions of people around him/her/they, specially their most loved ones. With this kind of knowledge, they could guide themselves or their team on how to act around others. In Meulin’s case however, she could communicate with Kurloz, her ex-matesprit, despite being deaf or maybe because he is controlling her with telepathy, and when he does he is revealing his true intentions, she is hearing his soul or his true self. Then speaking about the creation part, this could be either Meulin’s matchmaker abilities or the ability to create motivation/desire based on the things that that you know will motivate your game companions, which gives you some sort of manipulative abilities towards others. The dark side of this is that you may either end up in Meulin’s situation or have some sort of issue with being sensible towards people’s true feelings or even with yourself’s.
Mage of Time: A Mage of Time would probably be able to communicate, see or interact, with other iterations of him/her/themselves in other timelines or with other timelines and create an alpha timeline based on that info. You would have your time device and hop through one timeline to another, gathering all the information you can. The dark side to this is that most of that knowledge to create that one perfect alpha timeline would come from watching all the million dumb ways to die and create doomed timelines of your other iterations or timelines.
(wow, that was an abuse of the words “doomed” and “timelines”)
Well, I hope this somehow helped you. Choose on how you think or feel is closer to how you would affect reality. If you had the ability to time travel, would you use it like a Mage? Or you rather think of yourself as someone who deeply understands people?