Championship edit function

So I tried to start a new championship; Porsche Cup, 10 races. All went well, until I tried to edit the race length, quali etc. I could only race a maximum of 15 mins, in two races; I couldn’t edit from 2 races to 1; couldn’t increase the race length beyond 15 mins. Am I missing something here, this can’t be right. Does anyone know better, if these aspects can be adjusted? It’s difficult to believe they can’t be.
Thanks guys.