Although I am just an amateur gardener I would say that you could plant the hedges by the end of this month. The general time to plant trees and hedges, including bare root, is around this time of the year.
The Dulwich Cattery has now closed. Try Gloria on 020 8693 1533 - she is based in East Dulwich Grove. My son boards his cat there and has always been very pleased. Gloria is really nice and a real cat lover.
Try Dulwich Plants and Pots next to North Dulwich Station. They sell honey which is produced from the hives across the other side of the railway lines very close to their nursery. I have bought honey from there many times and it is very nice.