It's not an enormous garden, Geoff, couple of acres probably - no great distance involved, so it's about your individual style of looking at things. We had a whole day there, but that included looking inside the house, which is very interesting - especially if you like Japanese art, walking up the village for lunch at the Hotel Baudy, a look in the Musee d'Art Americain, and un petit hommage at Monet's grave. So I would think if you could stretch your three hours to four you'd be fine.
In September the garden will be a mass of colour from dahlias, 'big daisies', hollyhocks and so on.