At what point in a new job do u discuss flexible working or school runs?

At interview, just a question around working hours and working patterns is normal. Whenever I’ve interviewed, I’ve always explained the expected working patterns with candidates.

No point starting the process and wasting your time and theirs, get the answer you need asap to make the right decision for you.

If you need certain hours/times from the get go, I'd mention it in the interview.

If you need it later down the line, request it then.

If your in australia, then after 12 months there is a law about flexible working arrangements, i would have to review it for the specifics.

I would imagine before you even start the job. There should be a clear expectation on both ends