Quite a while potentially
Hi Larry
High temperature systems are advancing quite steadily, so a Venus rover should last for at least a month or so. The RTGs will need a bit of beefing up, but the denser atmosphere might improve convective heat-rejection and allow decent efficiency. Geoff Landis put out a paper design of a rover recently and I was surprised by the progress in materials and circuits operating in the 400-500 oC range.