The time function is the best function you should use for storage as time() records time in what is known as Epoch time (or the number of second that have past Epoch - Midnight January 1, 1970). This number represents the exact date and time of that instance. I would store the data in your DB (if you are using a DB) in this format and make it readable when you need it.
Here are some examples for you:
To output date as "November 30, 2004 at 10:55 pm":
$date = date("F j, Y at g:i a", time());