I discovered the that iPhone 4 has a max video recording length of 50 mins due to some limitation built into the phone. Is Windows Phone similarly limited?
I was able to record 43 minutes before it stopped, and that was due to lack of storage space. I have over 9GB of free space, so presumably the only limitation is the free space you have on your phone. I can't be sure of this though. YMMV
I'm agree with @Joe, But don't forget your have two limitations, your mobile free space (+1 @Joe), and your battery level!
If you have 1TO free Space, if your max battery recording for 1 hour, you don't recording more than 1 hour...