There are a string of pages prepared by the Mayo Clinic starting with this one that tell you a lot of good stuff about the nuclear stress test.
http://www.mayoclinic.com/health/nuclear-stress-test/
MY00994
And in particular, here's the page that tells you about what to expect ...
http://www.mayoclinic.com/health/nuclear-stress-test/
MY00994/DSECTION=what-you-can-expect
It's essentially a combination of a stress test and angiogram without having a cardiac catheter put up your into your cardiac arteries.
It says that when the test is done you can go on with your daily activities, and that of course is dependent on what they find in this test. If they do find anything that requires immediate attention they may ask to begin treatment then and there.
You should not drive yourself to the location for the test (usually because of the equipment needed it's usually done in a hospital or specialty clinic). Get someone to take you and pick you up later when done. This ensures that you don't have to worry about a car in case you're required to stay longer.
The actual treadmill test is quite the aerobic workout and lasts about as long as you can cope with the exercise without distress. My first stress test was over in about 5 minutes cardiac impact, and after bypass surgery, my second in about 7 with no cardiac impact (my legs were killing me!) and the third lasted 9 minutes again with no cardiac impact.
