Longer recording time is a comparative term, and it was used to compare a video camera with DOF adapter with a DSLR which gives similar shallow DOF but has restricted recording times due to file size limits. For example the maximum shot length with Canon 550D is around 10 minutes in 1080 mode.
Of course you will not get longer recording times from a PD170 by adding a DOF adapter (I suspect you know this already). Anyway do you really need to shoot continuously for more than 1 hour?