The functional prototype for mktime() is:
mktime((int) hour, (int) minute, (int) second, (int) month, (int) date, (int) year);
It will return the UNIX timestamp for the date entered.
To get the 'user-friendly' date back from a UNIX timestamp, you can use the date() function with a second argument:
date("d m Y", 1016553600);
Have fun