Evening Prayer used to be a a much more common feature of Anglican worship than it is today. You can tell just by looking at old hymnals (such as the Episcopalian hymnal of 1940) and observing that there are far more Evening hymns than Morning hymns. And several of the Evening hymns in the Anglican repertoire are absolute gems of English hymnody! If you’re an American under the age of 50, or new to the Anglican tradition at any age, chances are you’ve hardly ever heard any of these beauties before.
There are two points in our Evening Prayer liturgy where inserting a hymn comes most naturally. The first place is after the Invitatory: the Phos hilaron has a rubric above it saying “The following or some other suitable hymn or Psalm may be sung or said.” Because the Phos hilaron itself is a new addition to the Prayer Book (only dating back to 1979) we are well within our traditional rights to sing something else in its place. The second spot in the liturgy is after the three Collects: “Here may be sung a hymn or anthem”. This is the most traditional placement for a hymn, and is a great way to break up the formal collects of the liturgy and the additional intercessions and thanksgivings that may follow.
Might I recommend, this evening, one of the best of the best? The day thou gavest is a beautiful hymn, both musically and lyrically, reflecting upon the practical and theological meaning of the end of the daytime, awareness of the cycle of daily prayer across the globe, and the subsequent unity of Christ’s Church.