The instructions are to hold the magic button (the button in the middle of the bot that you press to turn it on) for 5 seconds. Since everyone estimates seconds a little differently, I do it for a count of 7-9. When you release the button it will flash colors and turn off.
However, if you're trying to charge your Jewelbot, you don't have to turn it off! Just take the flower charm off and plug it in. A red light will turn on, and then turn green when it's finished charging.