''how so? where and when did he (or anyone else in the bible) give a date for his return?''
A date is not given in the bible, but a clear time frame is described; within the lifetimes of generation who were standing there, that some would still be alive to see the return of Jesus in Power and Glory with the Angels in the clouds for all the tribes on Earth to see. This is what the first Christians expected to see. It did not happen.
