18 hours is 6am to midnight. Imagine spending that time sitting in a not very comfortable narrow chair with limited recline and a least one, quite possibly two people on either side of you.
J class one stop with a lie flat bed starts at around $7000, economy one stop starts at about $2000. A night in an airside transit hotel is around $300. If I was going with the wife in business class we're looking at $14000 vs $4300 for a comfortable trip. J class is great if someone else is paying or you've got money to burn. I'm taking the slower option and saving $10 000 by arriving a few hours later and I'll be less jet lagged.