Mythic Spell Focus and spells that last multiple rounds

[Goblin_Priest]

RAW: "Choose a school of magic you already have Spell Focus in. The bonus to save DCs provided by Spell Focus and Greater Spell Focus for that school increases by 1. You can expend one use of mythic power as part of casting a spell from your chosen school to force any of the spell's targets to roll their saving throws twice, taking the lower result."

I used a mythic point to force my target to roll twice upon casting hold person on him.

The DM and I aren't really sure as to how this is supposed to work. Does the effect only work on the will save to resist the spell, or also on subsequent saves to end the spell's effect?

[LazarX]

Only the initial save is affected.

[Goblin_Priest]

Really? "Saving throws" being plural, I didn't see anything suggesting it was only the first save, instead of all of saves provoked by the spell.

[GM Rednal]

I agree with you, Goblin_Priest - I would say that probably affects any saving throws provoked by the spell (since there's no limitation on when those throws must occur, only that they be from spells from your chosen school).

In general, Mythic Abilities that affect existing abilities - especially feats - are best interpreted in the context of the abilities they're attached to whenever there's a doubt about how they're supposed to apply. Spell Focus and Greater Spell Focus apply to all saving throws from your chosen school, so it makes sense that Mythic Spell Focus would likewise affect all of the saves.