Convert date/time to epoch:
http://forum.mikrotik.com/t/i-did-it-script-to-compute-unix-time/68576/24
add the required numer of seconds,
Convert back epoch to datetime:
http://forum.mikrotik.com/t/convert-uptime-to-date-and-time/157724/36
On those days I have just the time to reply on this way.
When I have time (and I remember this) can I check, but also other forum members can check and fix…