As you have learned in the last few lessons, The printed music is often just a starting point for the singer to learn a song before giving it their personal interpretation. One of the most common ways a singer will change the original timing is to hold a note at the end of a phrase and pause before delivering the next lyric. This is particularly common in ballads. The accompanist(s) will need advance warning, so they can pause along with the singer.
Sometimes a composer will write timing variations into the phrasing. In the following ballad, you will notice an occasional bar of % time (two quarter notes per bar). This is to give the singer two extra beats to hold the last note of the phrase. This brings attention to the lyrics in a way that would not happen if the timing continued straight ahead in * .
Listen to the recording and notice that the second time a % bar occurs, there is a definite pause by both the singer and accompanist. This is indicated by the symbol ? , which is called a fermata. Stretching or altering the timing is referred to as rubato. The amount of rubato is up to the individual performer. It is best developed by listening to the way great singers and instrumentalists use it. Once again, this involves a lot of listening.