I'm planning on buying the Madrid Tarjeta Paseo del Arte pass late in the day on a Thursday in September after arriving in Madrid, at the Thyssen-Bornemesza Museum ticket window. Does anyone know whether the ticket window closes before the museum closing hour?
I don't know, but the vast majority of the Spanish museums I've been to had the policy of halting entry either 30 or 60 minutes before the museum closed. If they aren't letting anyone in, there's a reasonable possibility that the ticket window will not be staffed.
According to their website www.museothyssen.org/en/thyssen/horarios until one hour before closing time.