IMHO, the definitively best and easiest way to handle date/time is to use unix timestamps. A unix timestamp is the number of seconds elapsed since January 1 1970 00:00:00 GMT. These timestamps fits into a regular int field in mysql, and can easily be converted to human-readable format using the PHP date() function. (i.e. date("d/m-Y H:i:s", $timestamp); will give "day/month-year hours:minutes:seconds").
Adding one minute to this is easy, just increment by 60. $timestamp += ((606024)*5); adds five days, regardless of months, days in months, leap years etc. Very easy to sort by, compare (i.e. if $ts1 > $ts2) { .. }) and so on.
You can also convert "human readable" dates into timestamps, checkout mktime(). SELECT UNIX_TIMESTAMP(field) in mysql might also come in handy. Hope it helped 🙂