It is already a problem on space shuttle missions, where the crews typically operate on days of 23 1/2 hours.

All were single horse operated except for 7 and 8 on busy days which could be operated by a pair.

In order to protect the instrument it is only operated during the summer months and on days when weather conditions are clear.

It is used mainly in winter months for engineering trains but does operate passenger services on selected days during the season.

Eventually the gangrene worsened and the doctors operated several times on successive days, but were unsuccessful.

There is also a collection of vintage road vehicles which are operated on selected days.

For several years, the community reached a deal with Falconbridge that the smelter would not operate on days when a north wind was blowing.

Steam operated passenger services operate only on selected days, mostly summer Sundays.

Only operates on certain days of the week.

With their air-conditioning cut back, surgeons say they are sometimes unable to operate on hot days.