Always On Listener Behavior - DBs removed from group
How large are your transaction log files? I'd be prepared to try going with leaving them disconnected, provided no reindexing, bulk ops etc go on during the outage, and provided you can be 100% confident it will only be 6 hours.

In my experience OLTP transaction log growth is normally modest, and provided your t-logs are a reasonable size, you should be ok.

Difficult to test though as normal OLTP transactional throughput is tricky to simulate, although profiling for replay could be a way of measuring it.