Roger,
I have been three times, twice in October and once in March. Our summer months coincide with their rainy season, and is not recommended. Many roads are unsurfaced, and I can only imagine what they are like following a bit of rain (let alone a LOT of rain). I think the mozzie situation would be much more of a nuisance during the rainy season as well.
I would recommend hanging on until October if you can, that way you avoid most of the rain, but the landscape isn't dried up and the bishops are still in their breeding plumage.