I have Premium an when I start with
https://www.windy.com/de/-Wolken-clouds?clouds,50.228,10.992,8,i:pressure
I have 14 days in timeline

Then I switch to visiblity I see 14 days - see picture start-_1.jpg
Good conditions in Coburg area.
https://www.windy.com/de/-Sichtweite-visibility?visibility,50.228,10.992,8,i:pressure

Then I switch to fog page
Now I have 8 days in timeline - see fog_2.jpg
https://www.windy.com/de/-Nebel-fog?icon,fog,50.228,10.992,8,i:pressure

Then I switch back to visiblity - see visiblity-3.jpg
Now I have only 4 days in timeline and different bad weather in Coburg.
https://www.windy.com/de/-Sichtweite-visibility?iconEu,visibility,50.228,10.992,8,i:pressure

The difference between visibility is ?iconEu,visibility an ?visibility

The days in timeline remain until I totally restart the browser from the beginning
Browser is Chrome or firefox the same