I made a better overview page
Much better layout but the Colour combination is unreadable!
This category covers sites that take 5 days to visit (including getting there and away, and be on the move to a next WHS f.e. at an international airport)
I have checked the island WHSites listed above and none of them has even an airstrip there or very nearby - Gough/Inaccessible, Macquarie, Heard/McDonald and NZ Sub-antarctic so there seems absolutely NO physical way of getting to and from them within 5 days as ship is the only transport means available -whatever it costs!
However there is an issue about some others which do have an airstrip or one nearby. In theory someone with with extra pull via direct access to the President of the country, a private helicopter, mega-mega bucks etc etc etc might be able to get to and from these islands within 5 days using these BUT as far as I can tell "normal" people could not!!
a. Wrangel. The Russian Miliatary seems to have an arirfield/strip there at the Mys Shmidta settlement (The AB refers to it). This article seems to describe recent activity http://tass.ru/en/russia/794880
. Perhpas Roman Abramovich mught get President Putin to allow him to use it but I have no evidence that anyone else could!! To all intents and purposes Wrangle is only accessible a far as I can see by ship - and this would take more than 5 days return!
We visited by Ship from the African mainland via the Comores (taking more than 2.5 days to get onwards to Mahe) but there is an airstrip at the nearest other island - Assumption. To get to Aldabra from there you would have had to arrange first a private flight and then for your yacht (!!!) to pick you up or for a charter yacht to be there waiting (In which case you might as well have used it all the way from Mahe??) We met a small group who had "pull" through the UK ambassador to the Seychelles and they had been granted the VERY special privilege of being met at Assumption by a research boat from Aldabra (and had promptly crashed it on the reefs at Aldabra due to late arrival and they had to hitch on to Mahe with us!!).
Regarding land based sites. There are some in Africa which I suspect would take longer than 5 days to get to/from by land from a city with an International airport BUT if one had loads of money and chartered your own plane to the nearest airstrip I suspect that all of them could probably be done within the 5 days - I think of eg Garamba, Okapi.
Finally I think of Sagamartha NP. If you fly from Kathmandu to Lukla you reach Namche Bazar on at the end of Day 2. When I did the trip one didn't pass the park entrance and pay the money until the climb out of Namche on day 3. Looking at the map it appears that the Park boundary is before Namche so I guess one could just reach the boundary, "tick" off the WHS and return to Lukla to fly back to Kathmandu on day 4!!! But would one??? Sagamartha NP is a 5 day plus visit in all practicality