The quickest I ever managed wasa little under 3 hours. However, I suggest we abandon this as it is unprovable and becoming dull, and the moderators will tell us off.
The real issue is whether Manston is credible as a London airport, which it is not, which is why the name "London Manston" was abandoned.
By contrast, having tried the well established London - Ashford railway commute, I can see why Lydd carries the "London" tag.