Free childcare question

Hello!

I have a question about the 30 free childcare hours that im hoping someone can help with.

Im hoping to get the free hours sorted for this September term. To do this, it says i need to start back at work by end of September at the latest.

Does anyone know how much work id need to do in September to be eligible? Could I just pick up one day of work in the month and then go fully back in October?

Hope this makes sense! Thanks in advance!