I think we first have to clear up that there are different types of responses in different countries. In the U.K., there are four levels of response.
Her Majesty's Coastguard has the primary responsibility for all search and rescue, much the same as the Department of National Defence here in Canada. They have a response time of 15 minutes. The Royal Air Force also has four search and rescue aircraft, which are helicopters. They also have a response time of 15 minutes. They respond in a different way in different hours under different circumstances, and they are in different locations.
Then the oil companies, as Mr. Wells has already explained, have what they call Project Jigsaw, which is composed of dedicated search and rescue helicopters and extremely fast vessels that are the primary search and rescue means in the North Sea now. In fact, the helicopters are now the secondary means of search and rescue for the oil companies. The vessel that gets lowered, the fast rescue craft, is the primary means.
To answer your question, there is no simple answer to your question. It varies. There is no doubt that the quicker the response in the evening, the better, no matter where you are in the world.