How to manage output time.

[dstonek]

I have some gif animated files containg some photos. Each one is output in a period I have previously defined. A loop allows the process no stoping.
I want to expand the show using php and geting the image files randomically from a sql table.
In other words I want to output random photos for two seconds.
I may use rand(1, my_max_code_#) to get a random image.
How do I control the time? Thanks.