A great comment from “matthewj” over at MusicaSacra.com:
…this is a personal pet peeve that I work on with my cantors and choir all the time: don’t close the books the second the final note has been cut off! Give the hymn a second to sink in. Could you imagine if immediately after reading the last line of the Gospel the Deacon slammed shut the Gospel book as though he was so glad it was all over? Sing the final note, wait a moment, then quietly and discreetly close your book. If the hymn is really a prayer, you don’t need to close it the second the prayer is done, as though you’re terrified that more prayer might be waiting and ready to come out of that book. Take a moment, a silent Amen if you want to think of it that way, before going on your merry way.