Nursery funding

My little one was obviously 2 in January and has had the 15 hour funding since last year (which equates to about 11 hours a week as it is spread through the year) I’m aware that in September the gov are changing it to 30 hours for eligible parents with children ages 9 months and older. From what point will this start for my boy? Would it be immediately from September? Can anyone tell me roughly what 30 hours per week spread throughout the year equates to hours per week? I’m hoping it’ll save me some more money as he does 3 days a week at nursery, gets his funding but I still pay £600 a month