If i took a break from my ipad to answer the phone and talked for 5 to 10 minutes, how do i get it to shut down in about 1.5 minutes. it did this before, and now it does not shut down. why?

First answer is right and to generalize these devices run and alter their states based on programming or programs running a do not dim screen command is part of running say like the netflix app. so you can watch without having to tap the screen to keep it on. like wise for power if there is a upgrade being installed the machine will stay on to complete it .
if there is a glitch in the programming that is being run then you get what you have . but fortunately you could unplug it and let the battery die overnite then plug it in and fully charge it before turning it back on once it has done house keeping turn it off and you may notice it is fine again. thanks for noting model specifics also.
I take it that it did not freeze just would not turn off.
my Galaxy tab S showed the little android guy on his back with a red diamond over his chest , below that it said no program chosen ,but would not let me do anything nothing worked and it would not shut off . well i started looking for my warranty information and decided that the battery would die and then i would charge and restart it. I did and it works fine today. programming and over ride corrupt programs cause problems and viruses . also light sensors . most all of this is fixed by factory resets and reloading apps and firmware updates. also there is a simple reset by paperclip in hole on side of pad i think 5 seconds but let it die charge fully and return on. if you had recently installed something take it out.

Set the auto lock for 2 minutes. Keep in mind that the iPad will not auto sleep and lock during certain application evolutions, like video, game application etc.

if it's just sitting at the spring board, it will auto lock at the specified time interval. imthemobile guru