While they use characters used are perhaps confusing, its merely flight time remaining while in flight. Next to that is RC signal strength, then obstacle avoidance status, the # of Sats and then the ellipse for the Fly settings. If you tap on the battery icon, you'll see the same 00'00" with more information while in flight, it will be all zeros if your not in the air.
There are slews of DJI Fly videos tutorials on YouTube, look for a recent one in the past few months using filters as the display does change as it gets updated. What they cover may change some from the current version of the app if you go to far back. But there may not be a tutorial with the absolute latest version, but there are always some that pop up for every version it seems with some channels version of whether they thinks its ok or they think they found problems.