I have discovered an exploit, it allows players to change the seed of a journey without restarting to London, I have only tested this on mobile. to do this, restart the game but do not click the begin button, then close the application and enter again. If done correctly, you would end up in a different seed with different things in the market and transport departure times. With this, I managed to achieve 25 and 26 days (the best known is 27 days which is confirmed by inkle), check in https://steamcommunity.com/app/381780/discussions/0/523898291513528978/.
London - Vienna - Warsaw - Moscow - Karimskaya - Pyongyang - Manila - Acapulco - New Orleans - Washington - Ponta Delgada - London.
Start with seed 6 or 7 (Preferably 7) due to the wine
From Moscow to Karimskaya, Change to seed 8, everything should be in good time and cheap.
The Brass Telescope from the Reina Christina will sell for ~£5500, then go to New Orleans, buy the Trombone which will sell for ~£3200. From there, take the train to Washington, to afford this journey, you must win the boxing match to afford speeding up the journey to Ponta Delgada.
In Ponta Delgada, sell everything in your luggage, then change to a seed which the "Six of One" costs £7100 and departs after the exploration time (10:30), even though it takes 2 more days to depart, negotiate through all of them, if you keep making money along the route, you should be able to afford the journey to London. if you found the six of one route in conversation, just cycle through the seeds and find the cheapest or the one you can afford
London - Vienna - Venice - Athens - Cairo - Suez - Khartoum - Stone town - Quelimane - Ulundi - Antananarivo - Rangoon - Batavia - Manila - Acapulco - New Orleans - Washington - Ponta Delgada - London
Start with seed 6 to get the wine price and the African airship timetable, until Suez, don't change seeds. Then on Suez, discover the airship to Khartoum then Change to seed 3, where the airship departure time is 3 pm, board it and you should arrive in Khartoum earlier than 11 am. Change to a seed where the ottoman geyik airship departs at 11 am. Sleep one day there and change the seed to where the Duala's Airship departs at 8 am. You should reach Quelimane at 6pm, then change the seed to where the Coppership departs at 7 pm, you should arrive at Ulundi at 11 am. Get the airship to Antananarivo and make sure Cetshwayo will contact the queen. Get the diamond shard from the polecat. Explore in Antananarivo and sleep, the next day, the queen will give you the option to fly to Rangoon by her airship, before boarding change the seed to seed 1. Go to Batavia, sell the shard for £6400,go to Manila then change to seed 8, and continue the game like the route above.
This explot could lead to routes faster than this