About Venus
As James Kasting, and David Grinspoon & Mark Bullock after him, have shown Venus becomes dry in about 500 myr if clouds are ignored, but with clouds the oceans of Venus could have lasted much, much longer. It might have only gone dry in the last billion or two years. Grinspoon & Bullock suggest that dessicating the mantle shut down slower modes of heat-flow and caused the catastrophic resurfacing regime that currently operates on Venus.
The new felsic rock finds might be datable and allow the question of how long the oceans lasted to be given a firm figure. The case for new landers to the Hell Planet has just gotten a LOT stronger - though by "lander" I mean balloons able to trek between the outcrops.