SharePoint 2007 allows you to define job definitions and schedule them, but you have to do it programmatically.
As it's impossible to change the job definition schedules from the UI, the preferred approach is:
- Define a feature that writes in the web.config the desired schedule
- Define a feature that schedules the job reading the desired schedule from the web.config
For second point, your friend is the SPSchedule.FromString static method, with returns an instace of a SPSchedule from a string that you can save in your web.config.
But how do you build this string?
You can refer to the definition of the method in the documentation page SPSchedule.FromString Method, that at the end of the page forwards you to the fantastic article SPSchedule.FromString(recurrenceValue) - syntax/format for recurrence value!