The TDBN route starts off from Fort William by going up the road to Blarmachfoldach, not up Glen Nevis – I’ve not travelled via the Glen or compared distances between the two but I expect going via Blarmachfoldach is slightly shorter and faster as more of that route is on road.
Let me know if you would like my gpx file for TDBN. A check of the results indicates most competitors finished in the 6-7 hour range, so it is a full day out.
There is a long stretch of carry from Luibelt north towards the bothy – the descent to the bothy was fantastic but tough on a hardtail.
If you don’t have the 6-7hours plus (factoring in stops, photo ops etc) then as suggested head east from Luibelt towards Loch Treig and on to Corrour to pick up a train back to the start. Or go to KLL via Blarmachfoldach and return via the WHW.
Slightly OT: Dewydd – did you drop anything on that journey the other day?