“so basically it needs to charge overnight to get that 315 miles then needs another 6 hours to do it again.”
In order to allow quick charging of Model S and Model X electric vehicle battery packs on longer journeys, in 2012 Tesla Motors began building a network of 480-volt fast-charging Supercharger stations. As of 20 May 2016, there were 624 stations globally, with 3,708 chargers.[1] The Supercharger is a proprietary direct current (DC) technology that provides up to[clarification needed] 120 kW of power per car, depending on location, giving the 90 kWh Model S an additional 170 miles (270 km) of range in about 30 minutes charge and a full charge in around 75 minutes.[2] A software update provided in 2015 to all Tesla cars uses demand information from each Supercharger station to plan the fastest route, if charging will be necessary to reach the destination.[3]
https://en.wikipedia.org/wiki/Tesla_station
From what I’ve read, the cars at supercharging stations might not all draw the full charging current. At a full 8 stall station only 4 of the cars receive the full charging current. The other 4 will charge at a reduced rate until the car in paired stall next to them finishes. Stalls are labeled 1A, 1B, 2A, 2B, etc. If someone is charging in 1A you would never pull into 1B unless all the other A stalls are full.