The kedusha is said as part of the morning blessings of shema, and also in all the public recital of prayers. It's not said in the evening prayer, neither in the blessings before shema nor the prayer itself.
Is there any reason why it's only mentioned in the liturgy (shema, shemone esre) during the day and not at night? Could it be that the angels only say the prayer during the day? Or is it related to the practice not to learn written Torah at night? Or some other reason?