Omnipresence requires that each point in creation (or space, if you'd like) is accessible to God with equal facility. More to the point, everywhere is actually always before God, though God himself is not circumscribed by creation or in any way actually "in" it. God, being God, is transcendent and immutable. In other words, God is what he is everywhere at once.
It is known that everywhere in space is in a state of fluctuation, nothing is static, everything is in motion and changing. To be omnipresent, God has to be the same everywhere despite everywhere's constant fluctuation. Change, in itself, is a time construct, but, thanks to Einstein, we know that time is experienced relative to motion. The result, I think, is that "this instant" is a much more fuzzy concept than I'd care to admit; nonetheless, it leads me to the conclusion that God must be omnitemporal if he is omnipresent.
Omniscience requires that everything that can be known is known by God. If, in any instant, God is unaware, or ignorant of some knowable thing, he would cease to be omniscient. Omniscience, it would seem, precludes discovery. If that is so, it follows that God knows all that he has known or will ever know at once, or at least at once upon any decision to act.
Knowledge grows with the passage of time. Not in the sense that new facts come to light as time goes on, but that new facts, correlated with time passing, come into being. There is constantly, in every instant, something new to know. The result, I think, is that God could not be perfect in knowledge if his knowledge was dependent upon time. Therefore (by definition alone), God must be omnitemporal if he is omniscient.
Omnitemporality is entailed in omnipresence and omniscience. We can't have one without without the others. To that end, God's omnitemporality could be understood to be that such that every instant in time is before God at once. God is not "in" time nor subject to it, but rather is transcendent to time and unfettered by it, and he knows its entirety from start to finish.