For anyone interested I've had a reply from Hempel as follows:
"The Data sheet information states a full cure of 20 days in a temperature of 5C, even that is on the generous side, the 10 days that yard state is more than adequate, the 45143 will have completely cured by then and be ready for immersion.
Your yard have coated many, many boats with our product and we feel they are one of the most competent and professional applicators in the Inland Waterways Market, we are confident that you won’t experience any problems".
I have to say Hempel have been very helpful and prompt with their replies.
Thanks everyone for your contributions