Extended minimum interchange times at Clapham Junction

[CheapAndNerdy]

I've noticed that journeys involving an interchange at Clapham Junction to South West Trains services now have a minimum interchange time of 20 minutes, instead of 10. Other interchanges seem to be as normal.

I assume that this is due to the impending major engineering works being carried out at Waterloo, but why implement the change 2 weeks early?

Example