time difference

i want to calculate the session time. my query is this

select now() - '2001-05-19 12:09:00+5;

it gives the difference in date and difference in time separately. if the
current time is greater than the second time then it gives simply their
difference but i want to calcutate the session time from these two times.
if now() = 2001-05-25 01:00:00+5
and second timestamp = 2001-05-24 23:00:00+5

then how can i get their time differernce EQUAL TO '3:00:00' instead of '21:00:00 ago' ?

and is there a way to get the total time difference including the date factor involved i.e.
if now() = 2001-05-25 23:00:00+5
and second timestamp = 2001-05-24 01:00:00+5
then is there any function to get their difference equal to '46:00:00' instead of '1 22:00:00' ?

please reply me soon.