Finally some time to follow up on this.
Charles, a listener, and James did experiments where they brewed the same beer with a 10 min, 30 min and 60 min mash. This was sparked by Chris Colby's comments on an earlier show that indicated that with modern malts a mash converts in as little as 10-15 min and that we don't need to mash for 60 min.
The result was that 10 min is way to short to mash. The efficiency of this batch suffered greatly. Interestingly enough it resulted in the highest attenuation in Charle's experiments but due to the lower efficiency the total amount of fermentable sugars produced was lower than for the other two mashes. Taste wise, Charle's 10 min mash beer tasted the worst. It was rather thin despite having had an OG of 1.063. The others tasted better and I don't remember if the 30 or 60 min mash beer ended up being the best.
I don't remember if James made drinkable beers or if he simply used bread yeast to test the wort fermentability.
The conclusion is that even though todays malts are said to convert in 10-15 min (which is a number that comes from a lab test) sufficiently long mashing times are needed to achieve the desired attenuation, efficiency and flavor profile of the beer. Even a negative iodine test
doesn't mean that mashing is complete.