Quite simply, all year round! Outside of the published social, training and race events members are free to use the water at any time. Its good practice to arrange with fellow sailors to have more than one boat on the water at any one time, for additional safety. A good way to arrange "buddy sailing" is to put a note on the bulletin board.
If you do sail outside of the events please sign the informal sailing book in the club-house and report any accidents. A life-jacket is mandatory all year round and you must wear a wetsuit or drysuit between the months of October to April inclusive. Stay safe and have fun!