When you are first studying and practicing to sing, you will want to be sure that you give your larynx, neck and face muscles, tongue, and vocal chords plenty of time to get used to this 'new' activity. It may not seem like it, but singing is both physically and mentally strenuous. Give yourself plenty of time to relax between vocal exercises, especially in the beginning of your sessions. Do not go beyond fifteen to thirty minutes per day. And, be sure to take one to two days off per week to allow all of these components to heal and relax. Resting for more than this will cause the elasticity of these areas to stiffen and tighten, which will not benefit you or help you add on to the work that you have already done. If you stop altogether for an extended period, do not put your voice through the stress or exercises that you were doing when you were at a certain 'peak' in your practice sessions. It will be best to start over, giving yourself weeks to become used to the activity once again.
A Note about Voice Strain:
The reason that we are talking about all of this is that is of the utmost importance. Not only is breath an important component of singing, but so are all the other facets that come into play. You want to allow your singing muscles the ability to steadily increase without allow them to become strained or overburdened. One reason why this course is laid out over 15 sessions is because you need to take the time to get yourself used to the transition that singing initiates if you are a complete beginner.
Also, if you have a cold or a sore throat, you do not want to injure your vocal chords or larynx when they are dry or brittle. It will be better for you to relax and heal before starting again.
Additionally, many singing instructors, including David Brantmoth, a renowned singing instructor in Europe says: "Practicing in the morning is the best time of the day. Your body and vocal muscles are all refreshed. Just like with any activity, give yourself plenty of warm up time and do not force a sound or pitch that isn't ready. After warming up, take your voice through its usual gymnastic routine. Only then should you attempt new material . make sure that you also cool down your voice each session."