Airbag bleed down

If you are leveling the coach (extending the stabilizing jacks) with an automatic leveler, the device will release all the air in the bags before extending the jacks. Don't confuse this with a leak. Good luck with your Tiffin Phaeton.

My bled down was my ride height value.

The air bags should stay up even if the dash gauges show 0 as they on a separate system controlled by three ride height valves. Even with air leveling mine will stay up for a month. If your coach goes down over night the good news is it's a big enough leak that you should be able to find it. Could be on the exhaust of the ride height valve that may require you to put your finger over it to see if it's leaking.
I wonder how long...?

Overnight is not ok. There's a water bleeder valve on the tank..that's usually the culprit.