Surrendering to God is not an event, it's a process. We can't say, "On day X, I surrendered everything to God, and that was that." We do make an initial commitment of surrender to Him. But, as in any other true love relationship, our surrender to our Beloved grows and matures over time.
My surrender and commitment to Him today is much deeper than it was two or three years ago. It's even deeper than it was last week. Yet the commitment and love I will have for Him one day will make today's level of surrender seem tiny by comparison.
And that's as it should be. Our gradually deepening "yes" towards God is a work of the Holy Spirit. It is He who woos us, He who challenges us, He who encourages us, He who prepares us for God's work, He who steadies us. Our periods of wandering in the desert (or sitting "corroding" at the bottom of a figurative swimming pool) very often even turn out to be God's way of making us realize our need for Him.
So yes, He wants to hear "yes." But He unfurls our yesses in stages, revealing both our own hearts and His own heart in the process.
He's in no hurry. He's in this union for the long haul.