"Now" is a specific place in the time continuum. You, me, the Earth, the dungeon... we all only exist in one specific place in time. We are not in the future and we are not in the past. We exist now. But Yog... Yog can shift himself a hair forward in time to where there is nothing but himself. No earth, no dungeon. He remains there, waiting. It's like you or I taking a single step left or right. You're not where you just were anymore.
Yog sits in the other time until he senses a strong mind nearby in space, and then he steps backward in time by one hair and SEES you!