In Australia the call back option should be working 9am to 6pm AET Monday to Friday, provided things are not too busy, at least according to that link.

If the OP missed the chance to use that option on Friday, it should be available on Monday.

Others may find the link useful as well, rather than arguing with the chat bot to try to get a call back link.

Call back hours are indeed different in the US: Monday to Sunday 5:00 am to 09:30 pm PT.