These days, most organizations that 'do' business continuity understand the importance of exercising and testing. Many have comprehensive exercising and testing programmes, which include crisis/incident management exercises, IT recovery tests and user relocation tests, amongst others.
It's not unusual for IT recovery testing to be done out of hours, in order to minimise any risk or impact to the business. The same is sometimes true of user relocation testing. But crisis or incident management exercises are almost always conducted during office hours.
The main reason is that exercising during office hours is more convenient, both for the participants and the facilitators, and there's usually (although not always) more chance of getting the key players to attend.
But exercising during the working day also has some distinct disadvantages. It doesn't, for instance, simulate in any meaningful way a situation where those key players have to deal with a major issue when they're already tired after a busy day's work. It doesn't test out of hours access to facilities or people. And out of hours is precisely when small incidents have a nasty habit of turning into bigger incidents, usually exacerbated by the fact that the right people aren't around to nip them in the bud.
Organizations with a mature crisis/incident management exercising programme should give serious consideration to carrying out the occasional out of hours exercise. This may be a little unpopular at first, until participants get the point, so rather than going the whole hog and starting your next exercise at 2am on a Sunday, perhaps a 7pm start on a weekday would be slightly more palatable.
There may be some moans and groans at first, but these are likely to be far outweighed by the resulting improvements to your crisis/incident management capability.