When you say quotes? What do you mean?
If by quotes you mean buy\sell orders, the price increased, and I then tried to sell, the price decreases and I tried to sell, and it decreased again. All of this happened within 5 minutes.
With regards to trading212, displaying a notification of the trading status. The system already has the functionality of this to extent.
If conditions equals true, then do something.
If no quotes within xyz time range, then disable trading.
This could be, if no quotes within xyz time range, then disable trading and set “market open” to “Market Open - (TS)”.
As for latency testing, a basic ping test would determine this, and I’m only using ping test, to get the idea across, and depending on the results Red, Amber or Green could be displayed as a notification next to “Market Open” but maybe trading212 wouldn’t want customers seeing this as this should be fixed behind the scenes to ensure this doesn’t happen (some kind of failover procedure to another server\network or what ever the case maybe).
Just my 2 pence
But when referring to quotes what exactly are you referring to? A trading platform should allow you to trade???