How long could you keep a medium sized, brown, healthy, 2 years old dog outside in full sun without water on a 95 °F (35 °C) day without risking sunburn/heatstroke/etc.?
Clarify from comment posted by OP: a dog was kept in that situation for an hour and a half, got into a debate about whether that was too long and went looking for sources for backup but none give a time limit. Argument was "well you take a dog to the beach, right?"