Yes, you can record any type of images without the motors armed.
And Yes, you can retract the landing gear on an H480 by powering it up and binding to the ST16, then invert it and toggle the switch to the retract position. Extending the gear is the same procedure, just flip it over and toggle the switch to extend them again.
Obviously if it isn't flying, you will need to suspend it from something to have the camera on it to record. You will have full control over the gimbal and camera, just as if it were flying.
Another benefit of retracting the gear manually is the aircraft can be powered off with gear retracted so can be easily strapped to a daypack/rucksack for convenient bike/hike transport with the gear retracted and camera removed. Much less cumbersome than the refrigerator with straps -AKA Backpack- that Yuneec gives us for transport!
I cannot answer the duration question, but needless to say it would be much longer without the motors ruining. I might guess 45 minutes maybe more, and maybe less if you have Real Sense installed. Let us know if you try it.