You said — “No. God has set the timetable. The time for return was already set before any of us existed, and only God the Father knows it. Because He knows the future before it happens, as God is not constrained in time as we are, the whole premise of ‘waiting’ isn’t quite the same thing.”
Yep! It’s already “pinned down” to the exact second, as to when it will happen — no matter what we will do — *because* God already knows exactly what each one of us is going to do, before we even know it ourselves...
It’s already determined. It’s just that we don’t know it — but God does.
It’s been said, “Israel is God’s timepiece”, as indicated in Matt 23:37-39, Lev 26:40-42, Jer 3:11-18, and Zech 12:10.
Mat 23:39
(39) For I say unto you (Israel), Ye shall not see me henceforth, till ye shall say, Blessed is he that cometh in the name of the Lord.
In another fashion, in direct answer to the question: what determines Jesus’ return to earth, technically every believer in fellowship with God through faith in Christ in the Church Age is indwelt by God the Holy Spirit, who provides a temple for the indwelling of Jesus Christ who is one with the Father. Today, for the believer, He is in us and us with Him when we are occupied with Christ while filled with the Holy Spirit.