You have developed your wings to last longer each day. 

• You can extend your wings as an action.
• Flying speed equals 30ft. (Yes this allows you to fly with the Fallen and Scourge Subclasses)
• You can use your wings each day a number of times equal to your proficiency bonus.
• The time your wings last each use is equal to your Con modifier + Proficiency Bonus multiplied by 6 minutes when not in combat. When in combat, each use lasts a number of rounds equal to your Con modifier + Proficiency Bonus multiplied by 6

ex: a Con Mod of +2 at level 5 (Prof Bonus of +3), multiplied by 6 = 30 Minutes/Rounds

DM note: The reason for having the difference between rounds and minutes is with the assumption of being in combat you are moving at a quicker pace and using more energy. It can be up to the DM to also have limits if the player Dash's when not in combat.