How detailed does the itinerary need to be?

My partner and I are currently traveling in S.E Asia and have flights to Hong Kong then onto Beijing in February. As UK nationals I know we don't need visa's for HK, but we would like to know how detailed our itinerary needs to be for the rest of China? Do we need to show hotel bookings for each city on each day of our visit as it will be a trip of around 1 month.

We already have inbound and outbound flights booked but would like some advise whilst we have time to prepare to apply for the permit which we are planning on doing in Hong Kong or possibly Phnom Penh.