I just killed Mad Mel in borderlands and I am a level 22 soldier how much longer in the game do I have time-wise completing all of the side missions along with the story

well, it depends. i completed Playthrough 1 at lvl34, and i literally just got done with every DLC, side quest, and story quest just a few days ago in Playthrough 2. With every single quest done, including DLCs, i have just over 2 days of in-game time.