1. You are required to visit all railway stations, including Tube, National Rail, DLR, Tramlink and London Cable Car stations, within the Greater London boundary only.
2. A station is defined to be either a single paid area, which may span across ownership boundaries, or multiple paid areas without crossing property ownership boundary. This definition is necessary to allow consistency across transport modes, which means:
2a. In the Tube network, there are two Hammersmith and Edgware Road stations and both must be visited, as they are not connected otherwise by street level. Bank and Monument are one single station. Farringdon and Barbican are one single station as they are connected by the Elizabeth line platforms. Moorgate and Liverpool Street (Underground and Elizabeth line) are also one station, but Liverpool Street (National Rail terminal) is another station. In the National Rail network, Hackney Downs and Hackney Central are also one single station as they are connected in the paid area.
2b. There are 3 Paddington stations: National Rail terminus, Hammersmith line station, and Bakerloo / District / Elizabeth line stations. There are 4 stations within the King's Cross St. Pancras complex: St Pancras terminal station, King's Cross terminal station, St Pancras Thameslink station and King's Cross St Pancras underground station. There are 2 Liverpool Street stations: the National Rail terminal and the Liverpool Street / Moorgate Underground / Elizabeth line / Northern City Line station. There is only 1 Stratford station consisting of National Rail, tube and DLR and only 1 Kentish Town station as both modes are behind the same gateline.
2c. Wimbledon is a single station consisting of National Rail, Tramlink and Underground. Elmers End is also a single station as there is no boundary between the tram and National Rail platforms. Mitcham Junction Tram and National Rail stations are separate as there is a property boundary in between, with tram and heavy rail being using separate fare systems, similarly for Beckenham Junction as well.
3. A visit is defined by departing / arriving the station on a train in public service. The train must stop there, except if an emergency prevents the train from stopping as scheduled, but there is no requirement to board or alight the train. If the station is closed for construction work with no train services serving it, passing through is acceptable. If the closed station is a terminal station, it can be visited by other allowed means.
3a. Some stations only have limited opening hours or services. This must be taken account into planning. For example, City Thameslink is only open Mon - Sat, while Sudbury & Harrow Road has a limited service.
4. Only travelling on foot or on scheduled public transport is allowed. Taxis, private hire cars, or any forms of private transport such as bicycles and scooters are not allowed.
5. You must stay within Greater London boundary within the whole challenge. Travelling outside Greater London, no matter on foot or on public transport, between stations is not allowed. In particular, you can't travel on the Crayford Spur as it is outside Greater London.
Using the above rules, is it possible to complete the challenge in one day? If not, how many days are likely required? Also, are there any better definitions of a "station" for a challenge involving multiple modes of transport?
[EDIT by tubeguru - I added some spaces between points, to make it slightly more readable
