I'm looking at some commuting options for work (Sailsbury-Pinhoe) as I'm sick of driving. Looking at National Rail for today just to see prices I note that there are advance fares listed. This is an attractive option, but I will only be certain what train I'm getting home once I actually leave the building. I was surprised to see advance fares listed at all for the same day, at what point before departure do they cease to be available?