I would suggest do a "prayer" kind of job. Summoners call forth the powers of mythical beasts to their aids, then let them have that...aid, not the actual pet following.
Example:
They can have summoner as a regular magic related, you are allied to Ifrit's believes for example, then It will give power to you(the user). You will have spells like Fire, flare, maybe comet, some sort of blaze spike, another sort of enfire, and so forth. then you have this limits, or 2hours (whichever you prefer) and those open a path relatively short for the summon to cross (or try to cross) just to assist with whatever power he can let through the insignificant portal we mortals make. He aids and leaves . . .(in my opinion) a summoner should be a blackmage blessed by it summon. (or so)
Example:
They can have summoner as a regular magic related, you are allied to Ifrit's believes for example, then It will give power to you(the user). You will have spells like Fire, flare, maybe comet, some sort of blaze spike, another sort of enfire, and so forth. then you have this limits, or 2hours (whichever you prefer) and those open a path relatively short for the summon to cross (or try to cross) just to assist with whatever power he can let through the insignificant portal we mortals make. He aids and leaves . . .(in my opinion) a summoner should be a blackmage blessed by it summon. (or so)