As long as they are in constant sun, 60 is pretty much the minimum. Go outside and stick your hands out. If you can feel the warmth from the sun, then it should be ok.
60 is fine.
Mine are out as long as it is above 50.
They heat up in the sun kind of like little bricks. Because of this, their body temperature can be much warmer than the air temperature as long as they have sunlight to work with.