Question: Is there a minimum/maximum time to warm up the vocal cords before singing?
Answer: No. Every singer and every body is a little different so you need to find out what works best for you. Phil Collins used to sit in a wet sauna and vocalize for 45 minutes before every show. Think of Olympic runners. They all have different routines they go through before a race. Also, sprinters have different warm ups and work outs than long distance runners, because there are different demands on the muscles and bodies for different types of running.
Your vocal style and the length and intensity of your performances will determine both your daily work out and your warm up. If you are singing one song it will be different than if you are singing for 3 hours. Also, if you are singing an aggressive style over a light style this will also affect your work out and warm up. Comparing to runners again, most times if a runner has a race later in the day he will often go out early and do a workout. He will then rest, then just before the race he will do a light workout and a stretch. Remember that whenever you work out or warm up the voice you should start slowly and then get more aggressive as the body or the voice warm up. So, make sure you are warming up the voice before a performance and not tiring it out.
Also note that marathon runners don’t run 26 miles every day. Usually the most they will run is 10 or 12 miles, then on other days it may only be 3 to 5 miles. What is important is that they are doing it every day. This is the same with weight lifters. They will do heavy sets one day, then light sets on opposite days. The heavy sets build the muscles and the light sets stretch the muscles.
In working the voice, frequency is more important than duration. It is better to do 10 minutes twice a day, rather than 2 hours once a week. Frequency and consistency is the key. Personally, I like to warm up for 20 -30 minutes on “work out days” (or even 40 minutes sometimes), days that I am not performing. On performance days I will do 10-20 minutes of a pretty good workout earlier in the day (at least 2-3 hours before the performance), then 5-10 minutes 20-30 minutes before I perform. Again, each singer must be sensitive to their own voice and find the routine that works best for them.
One last thought, most singers (and many runners) forget about doing a “warm down” after a performance. Warming down the voice, which is usually a very light “warm up” is very good for helping the body begin the recovery process. Also, remember that it takes water about an hour to work its way through your system and actually make it to your vocal folds. So, although drinking water during a performance is not a bad idea, it really isn’t helping your vocal folds too much right then, although it helps your throat and adds moisture to the general area. In order to get an immediate effect you must inhale the moisture so that it goes straight to your vocal folds.