c2.getTime().getTime() - c1.getTime().getTime()
1) This gives the time in millis.
2) divide by 1000 to get the total number of seconds.
3) divide the resulting number by 3600 to get the hours.
4) divide the remainder by 60 to get the minutes.
5) the remainder, now should be the seconds.
try using the modulo operator.