What you are describing does not sound normal for a non-rooted NOOKcolor.

If you want to let it go to sleep then do as @KryptoNyte suggests and set the screen to go into sleep mode after x minutes. Then a short press on the n button will wake it up and you can swipe the bar that appears to completely wake up the NC.

If you want to completely turn it off, press and hold the Power button for about 5 seconds and the screen will get blurry and a dialog box is displayed to ask if you really want to shut the NC off. If so then press OK. To turn the NC back on, press and hold the Power button for 5 seconds or so (should never take 30 seconds) until you see a line of text displayed across the top half of the screen. When the text is displayed release the Power button and wait until the NC restarts, which will take a while. Eventually the slider bar is displayed and you can slide it to wake up the NC.

If you are having to press and hold the Power button for 30 seconds each time to restart, then something isn't right.