I did a MR from MIA to SCL in Nov 2015 (on AA) where I arrived in the morning, spent a wonderful day exploring SCL and returned on the redeye that evening. Different than what you're doing but I remember the "security" to be pretty lax. On thing that irritated me is that I stocked up on water bottles at the Admirals club but an additional screening on the jetbridge removed water (since I was returning to the US).