As for what you will say, that before the economy Christ said this, but after the economy not anymore, when God rised Him and granted Him a name above all names. The Son hid it, saying that He didn't know, to the benefit of the disciples. Some other says, that, just as Paul says, then the Son also himself shall be placed in subjection to the Father (1 Cor. 15.28), not because there was a time when He was a rebel, but because not all His limbs have been perfected yet, thus, because Christ's body doesn't know that day or our, He says that neither does He.

Ὃ δὲ λέξει͵ πρὸ μὲν τῆς οἰκονομίας τὸν Χριστὸν τοῦτο λέγειν͵ μετὰ δὲ τὴν οἰκονομίαν οὐκέτι͵ ὅτε ὁ Θεὸς αὐτὸν ὑπερύψωσε καὶ ἐχαρίσατο αὐτῷ ὄνομα τὸ ὑπὲρ πᾶν ὄνομα. Ἀπέκρυψεν ὁ Υἱὸς εἰπὼν μὴ γινώσκειν εἰς τὸ συμφέρον τῶν μαθητῶν. Ἕτερος δέ φησιν͵ ὅτι ὥσπερ ὁ Παῦλός φησι τότε καὶ ὁ Υἱὸς ὑποταγήσεται τῷ Πατρὶ οὐχ ὡς ἀνυποτάκτου ποτὲ ὄντος͵ ἀλλ΄ ὡς μηδέπω τῶν μελῶν αὐτοῦ πάντων τελειωθέντων͵ οὕτως ἐπεὶ τὸ σῶμα τοῦ Χριστοῦ οὐκ οἶδε τὴν ἡμέραν ἐκείνην ἢ τὴν ὥραν͵ οὐδὲ αὐτὸς λέγει εἰδέναι. 

Cf. GREGORY OF NYSSA : Christ is always born in our soul ||| CYRIL OF ALEXANDRIA : Becoming Temples of God ||| MACARIUS THE GREAT : Overcome by Heavenly Desire ||| SYMEON THE NEW THEOLOGIAN : Becoming invisible and suddenly appearing ||| GREGORY PALAMAS : Calling everything near Him