Working with "time" data from MYSQL

Hi I have a MYSQL/PHP question for which I do not find an answer on the web. I have a MySQL table with a column of datatype "time". What I want to do is read the values from this table but display the database entries plus 6 hours. For example, when the database entry is 12:00:00, I want to display 18:00:00 on my website. I tried all kinds of tricks, with strtotime() in PHP and UNIX_TIMESTAMP() in MySQL, but I simply cannot figure it out. When I start with normal strings instead of times, it works fine in PHP, but I do not manage to convert the MySQL time data into strings. Thanks for any advise! Sebastian