I don't remember how long it took me. I was 12 years old at the time. I do know though that once you get use to it, when you aren't wearing your pump it is kind of like cutting off an arm.
When I take a break after using the pump for awhile it is the strangest feeling. I keep reaching for it when I get out of bed and if I roll over sometimes I will look for it trying to bring it over with me. I will feel very strange not having something in my pocket. I get over these feeling too but I feel like it takes me longer to get use to not wearing the pump then it takes me to get use to wearing the pump.
I don't think it takes most people very long to adapt and get use to it. However I am sure there are some people for which the transition is much hard then others.