When you look at the map of superchargers, it shows how many are working at your intended stop and how many are open. This info is pretty much real time because the Superchargers are all linked, via the internet and relayed to each user's Tesla. It is good practice to include any intended recharging stops into the route in your GPS. That way the car "knows" you will be charging in 15 or 20 miles and can start conditioning the battery so it will accept a faster charge. If I am sitting in my garage here in LHC and push the mic button on the steering yoke, and say, "Navigate to work", the GPS plots out a route from here to my farmstead in MT. All the supercharger stops are listed on the map and how long the charge will take. Within the last month, the car has started to do predictive availability of chargers, by taking in to account how many cars are headed to the charger, how long it will be until they arrive, and how long it will take to charge them. The main computer at Tesla uses all of this to show you whether the stall will be empty when you arrive or how long the wait will be, before you can start charging. Of course, the main computer also knows if a stall is down and can dispatch a tech to get it back online soon. 
One location on my route home has been kind of iffy for availability because it only had four 150 Kw stalls. I've always been lucky to grab an empty spot there but I have seen it full and others having to wait. I see that Tesla has recently installed 12 new stalls of the 250 Kw type there. That should fix that potential problem for guys traveling I70 through Utah.