PHP+Apache question

hey fellow php fans :) i wrote a php script that fetches some information from warious places on the web and stores the data in a mysql database. tho the execution can take a long time, so i would want to execute it on a regular interval instead, so the data can be fetched from the database only, with close enough up-to-date information. however php (of course) executes scripts as they are accessed, and i havent found any hints of how to accomplish this in either php or apache documentation. is there a easy solution? /Martin Lindhe