How do you answer the idea of timelessness is a Greek philosophical concept, not a biblical one?   

While Pythagorus, Parmenides, and Plato developed an advanced concept of timelessness well before the concept appears in the theology of the church, the idea is not without biblical precedent:

That God existed “before” time (1 Cor 2:7) does not make sense apart from the idea of timelessness. Note, for instance, Augustine’s commentary: “If you are before time, it is not in time that you precede it. If this were so, you would not be before time.”

The certain nature of God’s decree at a minimum strongly suggests timelessness (Eph 2:6).

God’s other attributes also seem to reflect both a quantitative and a qualitative distinction between man and God. His immutability, especially, seems to demand the absence of temporal succession.