Dear PJ,

Another reason why they're great - you need do nothing more than you already were.

Don't make any loud noises or sudden movements. Cacti are shy, especially when blooming, and like to be left alone. Pretend you don't notice their colorful display, and they'll put on a grand show.

More seriously, how long flowers last varies greatly from genus to genus. Some flowers open late in the evening, stay open all night and day, but are spent by the second morning. Many open only during the brightest part of the day, but close up again the afternoon. Each flower may be able to do this for 3-5 days. If it's cloudy, they may not open at all. Some cacti only bloom at one time of year, and others can keep on making new flowers for months.

How long the flowers last depends more on what the plant is, and less on what you do. Please, make as much noise as you like. :)

You don't need to do anything when the flowers have opened. Low temperature will generally increase their lifetime, some of mine last for 1 day in hot weather, but 2-3 days if it is cold. Some refuse to open in cold and/or cloudy weather though.
The most long-lived can stay for up to 14 days. The buds are more tricky, some species abort them if they don't get enough water, some abort them if they are too wet or for no obvious reason at all, and other species don't care much, they keep their buds no matter what you do. It depends on the genus/species.

Oh paracelsus...I giggled at your post. I had an instant image of a sheep when I read it.

Hehe...I love sheep...