1 day = 86400 seconds, thus one second = 1/86400 days. Adding 1 to a date adds one day. Thus adding one second by adding 1/86400. To add 10 seconds, just add (1/86400)*10 = 1/8640.

select sysdate + 1/8640 from dual; // this returns sysdate + 10 seconds.

I found TIMESTAMPADD in a SQL reference, but I couldn't get it to work and couldn't find it in the data dictionary.

Good luck!