I have just completed the Lee Valley Way in 9 hours 31 minutes 32 seconds. Due to some poor signage and getting lost the total mileage was 55.6 as opposed to the expected 53.
Use this link for maps: tfl.gov.uk/modes/walking/lea-valley
The signage is all pretty clear apart from between Welwyn and Hertford. It is a good idea to take the maps though or I can give you my gps route to download onto a watch.