how long should it take to download a 3.5 gb movie to my ipad?, how long should it take to download a 3.5 gb movie to my ipad?

How fast is your internet connection?

Depends entirely on your available internet bandwidth.

It would take me several hours on 3G mobile data

It does take a while, maybe less than an hour on mine. You could rent the movie and then delete it after watching it as this frees up space on I pad.