There are several reasons for a boil and the boil time.
- Hop utilisation.
- Driving off unwanted volatile compounds
- Concentrating the wort to increase the gravity.
- Coagulating proteins to help clear the beer.
- It also gives us the chance to play with burners and pots and stuff. (My favourite reason)
60 to 90 minutes allows all of these to happen at a rate that is easy to achieve and is reasonably economical on time and energy.
I go for 60 minutes because I like to reduce my brewing time if I can. I can also get the reduction in wort that I need in that time scale.
If you need to reduce more or do not have a set up that can manage the requirement that you need then go for 90 minutes.
As always in brewing there is rarely a definitive "right" or "best" way. It depends on the equipment, the recipe and most of all. How the brewer wants to do it.
Have you noticed that on asking a question about brewing you are more likely to get an opinion than and answer.