The cycle of the day relates to the cycle of the creation of the world. The act of creation is Hashem limiting His light in order to make ‘place’ for creation, Kabbalah calls this the Tzimtzum. Immediately afterwards Hashem started perfecting the world by bringing some Kedusha back into it and building up the world. The same cycle takes place on a daily basis.
This first step of creation parallels the time of Mincha. Starting from Mincha time the light of the day starts going down which parallels Hashems removing His light from the world. The Gamara says that the ideal time for Mincha is Bain Hashmashos, the time between day and night. The reason for this time is that it is most representative of the Tzimtzum since that is when the light finished being removed right before the world started being perfected.
This comparison explains why the Mincha prayer has only Shmone Esrey while Maariv has also Krias Shmah. The reason for this is that Shmone Esrey is prayer, is the Bechina of emuna, and Krias Shmah is the Bechina of bringing in Kedusha back into the world. Also the Tzimtzum cannot be understood therfore one can only use emulated and prayer, but what comes afterward can be understood and therfore it is appropriate to bring in the Kedusha by reciting the Shmah as we do at Maariv time.

(On a side note this explains how our times before Mashiach we are in the end of the sixth thousandth year of creation which relates to Friday shortly before nightfall which is this time of darkness as discussed above)