"The length of time that one can spend singing varies greatly from person to person and is dependent on a myriad of factors," Dean Southern states. Every BODY and VOICE is different. Throughout history, many great professional singers state that they spend just as much if not more time mentally practicing than physically practicing singing. Mary Garden, Debussy's Melisandre of the 19th century said she "sings it over mentally time and time again, studying harmony, phrasing, and breath so that I know it inside and out when the time comes to sing it." Another great dramatic soprano of today, Christine Brewer, balances her practice between singing and study of the score and translation.
It makes complete sense to spend just as much time with the text of a song or role as one spends with the melody and rhythm. When you really KNOW what you are saying, the phrasing falls in to place easier and you are truly communicating the song. You absolutely need to spend time vocalizing and knowing how to sing the phrases with proper technique, but you also can accomplish so much by score and text study!
Gyorgy Sandor, a great piano pedagogue, states in practice we can "go through the motion mentally and the sequence becomes automatic: there are no wrong notes, no fear of a section, and we (sing) play with feeling".
Dean Southern further expands that when mentally practicing, we use our conscious mind to do 5 important things: Align our Body, Breathe, Relax the Jaw, Control the Tongue, and Work on Our Stage Presence. Nothing can physically get in our way as we are not producing sound, but focusing our minds and bodies and imagining the sound, phrases, pitches, everything happening! If you hear it correctly in your head when mentally practicing, then when you DO sing it, it will be well-rehearsed and beautiful.
Mental practice is "intelligent, effective, and efficient practice" which is a true bonus and compliment but not a substitute for physical practice. Add some mental practice to your weekly practice sessions and see the difference! Happy Singing!