No. It is not contrary. This going to be a little pedantic, but I'm going to try to get you to look at the more pertinent issue: the person of Christ.
The two things you asked about don't directly have much to do with each other. The comparison is incongruent. What I suppose you are asking is that because Christ did not know something that God the Father knows, then is God divided?
To obtain proper perspective on this, you have to make some decisions in your line of reasoning. Your decisions influence your answer. My primary assumption is that the scriptures agree perfectly with each other, even in cases when we cannot immediately understand the harmony. In this regard, we must keep in mind the opening chapter of John.
In John, we read that in the Beginning was the Word. The Word with God and the Word was God. We also read that the Word came in flesh. That's the entire point of Christ: God, the one who made everything, came in flesh. Being God, He has all qualities of God, including omniscience. Yet, there is something He admits not knowing. So the proper question is not whether or not this verse is contrary to trinitarianism but rather "is it contrary to the claims of Christ being God, or is there disagreement between Matthew and John?"
Why ask it this way? Because there's nothing in our language and understanding of the trinity that directly says that in order for a person to be part of the trinity, he must be all-knowing. Instead, what we have is transitive understanding of omniscience being required in order to be in the trinity: you aren't in the trinity if you aren't God, and God is omniscient.
And so the answer is: either Christ was all-knowing, or else he was not. If not, then he was not God... except that John says he was. So if he did not know the day or hour, then he was not God. If he did know the day or hour, then it seems that Matthew's quote was wrong.
And here is the fundamental point: The scriptures claim both; Christ is God and Christ didn't know something. The problem seems to be that there is something incongruent about the person of Christ.
In history, the church has opted not to call this incongruence a contradiction but rather a mystery, one that is abstracted by the hypostatic union. We can only conjecture how Christ did not know something yet was still able to be called God. It's not even that there aren't good theories about how this is possible, it's just that it is indeed conjecture because the scriptures don't speak to it.