We just used this service it yesterday; the stopover time was estimated to be 21 hours.
The immigration process took really, really long—much longer than in other countries, e.g., Oman or Sri Lanka. So even with no luggage to collect and being from a country that gets a transfer visa, we spent a really long time at the airport just waiting in line.
We selected a 5-star hotel from the airline’s catalog. We arrived after check-in time, but there was no room ready at the hotel. So we asked for luggage storage for our cabin baggage. The hotel advised us not to store expensive items like laptops in their storage and they didn't want to store anything at the reception. As a result, we waited for the room until 5 p.m. In the room we discovered that the safe was not working. However, we didn’t want to lose any more time by asking for assistance at the reception, so we just left with our valuables in the room.
We took a taxi to the National Museum and arrived at 5:30. The museum was the best option since it closes at 7 p.m. Unfortunately, they started asking people to leave at 6:45, so the actual time we spent at the museum was only 1 hour and 15 minutes. Afterward, we took a 20-minute cruise to see the skyline.
The next morning, we had to get up early to catch our flight. An airline employee told us to arrive 3 hours before the flight, even though we only had cabin luggage and already had our boarding passes. We thought this was crazy and went there 2 hours before the flight. The airport is huge, and since the little train isn’t always running, you need to account for walking time.
We found out that the flight was delayed by 3 hours—not really enough time to go back to the city to do anything. So we spent the additional 3 hours at the airport.
When the 3 hours were up, the flight was delayed by another 90 minutes. In hindsight, it would have been enough time to go back to the city if the airline had given an accurate estimate from the start.
I would only do this again if my first flight arrives very early in the morning or if the second flight leaves very late. With a flight arriving in the middle of the day, it was not a worthwhile experience.