Mebe your mean is somebody waiting for you a few minutes or few hours in a place,you was just over there,but you don't know how much time he's waiting, then you can say:你在这儿多久了(How long are you here?) .and other, somebody and you are in a company worke together,he is at company early than you, you want to know how long did he stady here ,then you can say"你在这儿多久了"too.

ebe your mean is somebody waiting for you a few minutes or few hours in a place,you was just over there,but you don't know how much time he's waiting, then you can say:你在这儿多久了(How long are you here?)

你在这里多久了

it can be" 你在这里多久了“

the most correct way would be 你在这里多久了？（how long have you been here）do not try to translate "are" into 是. many times just ignore it when translate.