//…would you have had enough time left over to venture to Battersea?//
Plenty, jno. When I completed the Challenge there were 276 stations. The Victoria Line only ran as far as Victoria and not on to Brixton as it does today; The Piccadilly Line finished at Hounslow West, construction of the extension to Heathrow had not yet begun. However, the “Northern City” line (Drayton Park to Moorgate) was still part of the Underground, as was the East London Line (Shoreditch to New Cross/New Cross Gate). These branches have since been transferred to National Rail and the Overground respectively. The Bakerloo Line ran out to Watford Junction (truncated to Harrow & Wealdstone today), the Central Line extended by a shuttle from Epping to Ongar and the Aldwych shuttle on the Piccadilly Line was still operational. This meant there were 19 stations to visit which are either not open at all or not part of the London Underground (though of course extensions and new lines since then have kept the total roughly the same at 272).
Most of these presented problems when planning my route because Shoreditch station only opened for a very short window in peak hours, likewise Aldwych, and Bakerloo Line trains only ran beyond Harrow & Wealdstone to Watford during peak hours.
When I did my challenge the record time (which I did not beat) was 16hrs:5mins. Today it stands at 15hrs:45mins, though that was set in 2015 before Nine Elms and Battersea Power Station stations opened.
BTW, Battersea Power Station station is the only railway station in the UK to have the word “Station” in its title. :-)