Depends on how hot the temp is outside. Today the temp outside was 79. The concrete in the sun was between 96-102, in the shade it was 77-83. The slate was 111-125. I check it with my temp gun before I put him out, then a few times while he's out.
Just be sure there is always access to shade.
If it gets too hot, I spray the enclosure down-he loves that too!