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