When to harvest?? (uk outdoors)

I started growing in the uk outdoors and my plant is slight stunted in growth but has a bud i am scared that as of thecold and rain i will ruin my bud can anyone tell me how long i have till harvest or even should i harvest right now??

from what i here its not nice weather there at the moment,,,but your darlin is not ready for harvest yet im afraid...i said fuck it and dug my last few up and brought them inside to finish,,,,which is not a good idea ,but it is better then frost and mold..

atleast 3-4 weeks more