I detest a 5-8 hour overnight layover in an airport and would never willingly do this when other options are available. It's almost always the cheapest connecting option for a reason - it's long enough to feel like you are wasting time by the end and getting desperate to leave but short enough to make sure you can't use it to get a proper rest/night's sleep. The only way to make it bearable to me is to leave the airport which seems to defeat the purpose in this case if you really want to spend the time in the lounge. I'd go with 2 hours, but if this is your only chance to visit Al Mourjan and you have the time I'd probably still pick a 20-hour layover with a hotel room above the 8-hour one.