According to the DPReview here:
Panasonic Lumix DMC-GH3 Review: Digital Photography Review (http://www.dpreview.com/reviews/panasonic-lumix-dmc-gh3/8)

When recording video via WIFI, the camera will record only for 3 minutes or less. Is this true? TIA

No, but it take a little delving into the tablet/phone software to find the record time limit settings. It defaults to 3 minutes but you can change it in increments. The last I played with the wifi software controller I set the camera to record 20 minutes for an interview I was using the GH3 as a second angle. I ended up not using the wifi controls as the GH3 was eventually set up right next to the main camera. They programed a shut off timer as the wifi software strangely has no manual record stop control programmed in.

Sigh! That's an incredible oversight. I want to use it exactly as you describe... second angle for an interview... start and stop along with the main camera.

The software works nicely in a controlled situation but yes, a stop control would be really great. There has to some reason it's not there.