It keeps TG fit, the exercise will probably help the bone heal. There's a possibility that he could still beat the record this year because it reduces the amount that he falls behind the schedule. And, probably most importantly, if he does decide to run a parallel attempt starting in the summer (say 1st July for neatness) it means that he doesn't have to go from zero to 300 miles per day.
So, like pretty much everything else TG has done this year, it shows someone in full control of their faculties making practical and sensible plans.