Arrival day is always Saturday, anytime after 3pm. Of course it is possible to deposit bags earlier in case of early arrival, however the flat can only be handed over after that time.
By car, drive from Berne in the direction of Interlaken. After Thun, follow directions to Zweisimmen then Lenk. The second village after Zweisimmen is St Stephan, which is spread out over several centres. Continue along until you see a Bakery and tiny Shell petrol station on your left. In between the two is Byfanggasse. Drive up-hill for about 500 yards until there is a tiny road on your right (just after a small fountain), to Bifang 1-10. Chalet Strubeli is the second house on your left.