Conceptual.,

when f is the resistive force... here is the solution.. how time of ascent and descent is not equal in case of resistive force..

Yes, time of ascent is equal to time of decent. To see how follow the file attached.

yes, time of ascend is equal to time of descent. And the reason is, acceleration due to gravity is same for both cases. Also in ascending case, final velocity is zero. And in desce...

time of ascent is equal to time of descent only when there is no resistive force... so alwys not equal... I attached a page where time of ascent is equal to time of descent (means...