Simply by subtracting the 2 timestamps will give the number of seconds between the two. Then use a bit of arithmetic.
Say you get 125497 seconds.
125497 % 60 = 37 //seconds
(125497 - 37) / 60 = 2091 //minutes remaining
2091 % 60 = 51 //minutes
(2091 - 51) / 60 = 34 //hours remaining
34 % 24 = 10 //hours
(34 - 10) /24 = 1 //day
So 125497 (hopefully) should be 1 day, 10 hours, 51 mins and 37 secs.
Garth Farley