This is hard to answer because some of the factors that determine the number of road hours aren't given. We would need to know route, how fast you drive, if you plan to stop overnight or travel straight through. At the very least it would take 2-3 days of 8 hours of driving.
20 hours
The shortest time is 28 hours..
about 2 hours, but it depends on what part of los angeles
A little over 5 hours
2 hours
5
It takes 22 hours, 7 minutes and 49 seconds to drive from St Louis to Phoenix!
One hour
22 hours
The shortest time is 39 hours.
5 and 1/2 hours
over 5