PHP configs do have provisions for max execution time and also resources they are permitted to use e.g. max memory.
You can set these programatically.
See http://www.php.net/set_time_limit
It is not possible to set the limit beyond the environment max_execution_time - that is set in the php configs.
If you are on a shared server - these limits are often set quite aggressively to ensure resources do not get monopolised.