Hi Rob,
No experience re. an investment property but my last PPR was revealed to have subsidence by the Surveyor acting for the purchaser's lender. To cut a long story short, from diagnosis to remedy took seven months but that was after we made a huge effort to become friendly with the guy in charge of the works (we'd already found the property we wanted to move into and begged!). We were told that usually the property would be monitored for six months to assess what work needed doing, ie. does it need underpinning or just "sticking together", but fortunately they agreed to do the remedial work without monitoring it first. This was helped by the fact that they identified the cause very quickly, assessed the damage so far, and were confident that the property did not need underpinning, but merely bolting together.
From my experience, I wouldn't like to be depending on a maximum six month timescale.
Best of luck with it all.
Rowan
Stockport Property Solutions
www.stockportpropertysolutions.com
07950 568949