The race itself is about 1 1/2 hours to 2 hours. The tracks are not ovals and are 1 1/2 to 2 1/2 miles long and have grade changes. You do not win by going faster (all the cars can top 250 mph if desired), but by gearing, cornering, handling and most importantly, by braking at the right time.
They usually are about every two weeks (Wed. to Fri. practice, Saturday 3 qualifying segments when the cars are wrapped up and not touched until race starts). The start is usually about 1:30 local time on Sunday.
The schedules vary depending on the race location because when you fly 1 or 2 747s for a 2 car team with maybe 100-200 technicians/engineers, the races far from Europe (Australia, Malaysia, China, Japan, Korea and Brazil) they may run 2 weekends in a row. In Europe, they have to work around the country holidays. The U.S. lost the race because of the track and when there was more money elsewhere. The big money goes where the markets are.
No refueling is allowed during the race and the 1200# cars have governors set at about 19,000 rpm for the little V8s depending on the track layout (hills, etc.). A tire change (mandatory) takes about 4 seconds, but they lose more just to slow down.
It is a big dollar business with lots of technology and the drivers are really on-board engineers with big input. Just to put the cost into perspective, a car will usually have brake rotors on hand at a cost of $260,000 available for a week-end.
There are also the Le Mans type races that are 12 to 24 hours, but the budgets are much lower.
It is much better to watch on TV because of the track length and layout, but the act of being there is impossible if you can even get a ticket (usually $200-$800 if they are available). Scalpers are much higher as are the lifetime boxes.
It is not your NASCAR.