It makes sense that the sequence that begins with evening and morning would continue with noon. "Tzohorayim" means noon in both ancient and modern Hebrew. But you already know that the suffix "-ayim" doubles the word, as in "yadayim," the plural of "yad" (hand).
So what is "tzohar?" Even though the word is spelled with the letter tzadee at the beginning, it is actually the same word as the familiar "Zohar," the essential book of kabbalah. We usually see Zohar translated as "the Book of Splendor," but that name comes from the expansion of the more literal meaning of brightness and light. In fact, both zohar and tzohar can also mean "window," the portal in a wall that allows the outside in and the inside out, giving another layer of meaning to the mystical text.
The compact way Hebrew expresses ideas gives this word a good deal more intensity than the English word "noon," which comes from the Latin "nona," meaning "nine." Tzohorayim means "double-brightness," that time of the day when the sun is at the highest point in the sky. On a cloudless day, it is the when we see things with the greatest clarity.
So is this phrase "erev vavoker v'tzohorayim" (evening, morning, noon) just a poetic way of saying "always?" When we talk about the blessings for which we are grateful to God, can we make a distinction among the blessings of evening, of morning and of noon? Or could it be that we see the same blessings differently in the variance of light that the dusk, the dawn and the daylight bring?
It is reasonable to answer yes to each question. Of course it is ambiguous! Not only will each of us read this and other phrases in the prayer book with our own perspective, we each will also read this phrase differently at different moments of the day and of our lives. The only thing that is consistent among all the times of day and all the readings of this three-word description of the day is the constancy of God and the extraordinary wonderments God provides. That is to say, we should always be grateful, we should be grateful for the uniqueness of each time of day, and we should be grateful that God's gifts hold special meaning as the light fades, as it reappears and even in the stark clarity of full brightness.