Timing out if no output to screen

How can I stop scripts timing out if theres no output to screen for a while? Its not a script error timeout - it just stops loading in the browser.
I've got some scripts though that do some very long queries and if nothing gets output to the browser it stops - and doesnt finish executing the script sometimes.
I really need to fix this issue as it is causing major problems in my application.

I've just created a script with the instruction

sleep(900);


After 205s it said "You have chosen to open 'script.php'" with the standard download box.

my apache timeout is set to 600 as is the KeepAliveTimeout

I don't believe there is a why to do this. Maybe there is a way to replace the standard php message to something more appropriate for you.

There is no message - as I said - its not a standard php script timeout - it just stops executing.