You aren't going to complete an ETOPS check in less than an hour. Also keep in mind that ETOPS MELs are significantly more restrictive. Things that could normally be deferred can not for an ETOPS flight. So if an ETOPS bird comes in from DEN and the crew writes up an item that affects ETOPS it will either need to be fixed or another aircraft will need to be found. Southwest would be smart to build in buffers for repairs.