Tesla Supercharger

There's a few factors. As you mentioned, the number of people charging at once is definitely one of them. The station as a whole can only provide so much power, so if enough people are charging at once then it'll start to slow down. Another big factor is how much charge your car is at and what year/model you have. The older models don't charge as quickly at higher battery percentages.

Before you arrive to any Tesla station there is live data present with how many active stalls and even with how many are currently in use, seems like an odd question with my current model for obvious reasons, so maybe call Tesla support regarding that concern as you shouldn't have to ask through this input process.

Hyatt Regency

Depends what Model car you have and if you are on the same number as someone charging next to you. (eg. 3A and 3B) .if you started charging after you will be changing at a slower rate. I have an older model S and I charge at 90 kw/h ~300mi/hr. This station is 120 kw/h station so it will be higher than 300 if your model supports that rate.

I have been to over 181 different Superchargers in 6 different countries and never have I witnessed a non Tesla's ability to charge. There are countless chargers that you can pay to charge a fiat. Check with Charge Point or Blink