The cooker was set to high... and, as we needed the potatoes for lunchtime, we left them on high for about four hours and they were done.
The pot was switched off at this stage and care was taken removing the potatoes as they are hot and very soft. We found some tongs worked well.
A good amount of butter and some freshly ground black pepper were added and our meal was ready.
We have tried this when going out for the afternoon - starting the cooking off on high for about an hour and then reducing to low for the remainder of the cooking time. We find 4-5 hours will cook the potatoes through but, obviously, that depends on their size and also the power of the cooker. Ours is a very basic, 3 litre cooker with settings labelled as High, Low and Warm.