I'm saying that's something I would compromise on (probably having the default as 150% of the actual minima would be about right for most occasional users, with a quick option to set it to 200% for those of limited mobility but not requiring assistance), but I do think with journey planners being king now we could be more sophisticated with the actual minima.
With regard to the Forum site/Trainsplit, by the way, it would be handy if you could set the added time for specific stations when in "expert mode" - sometimes you just know a given connection will miss and want to extend that one to the train half an hour later but not the others. Not an issue on walk up tickets, just travel at the other time, of course, but for Advances you can end up with something that's almost guaranteed to miss with potentially more limited onward options (due to the same-TOC rule) - that is all very well in terms of if getting a free or half price trip is your priority (via Delay Repay), but most of the time I just want to make the journey as booked, not half an hour or an hour later because of a missed connection.