You cannot do that with PHP standalone.
What you need is a so called "scheduler", which usually is part of an Operating System. The scheduler triggers the desired programs at a certain time.
In Linux environment you may use "crontab" to start any job at any time you need. This i used for periodically repeating jobs. If you want to start a program once, you may use the "at"-Command instead.
Both (crontab and at) may be used to trigger a PHP Script which generates the Output for your needs. It does not work vice verse to run a PHP Script, which triggers any job at a certain time. You cannot run PHP Scripts endless in a loop (what would be necessary) and you cannot "awake" a PHP by itself - it must be started by a system service (or daemon).