Lee,
You need a minimum of 300 hours if you want to Instruct back in the UK and a good figure would be 500 to 1000 for this and other types of work with as many turbine as possible, what type of work are you looking for? What are working as at the moment?
Not sure about North Sea as it can change all the time, best give them a call, but seems a lot of peolpe are getting JAA IR(H) these days before applying!!! Loads of Money!!! Cheapest £28K.
No real good time if theres a job, Spring is generally better.