I used this malt (Chevalier) for several ordinary and special bitters when it first came back out 5-7 years ago and I liked the results. Out of an abundance of caution, I went with a longer mash regimen of 90 minutes when used on its own with a touch of crystal, but when I mixed it with some regular pale malt blends for other English styles (milds or pale ales), it converted well enough in a 60 minute mash regimen. I only had one full sack that I went through, so I can't say if they have changed the malting since the initial release. I would follow the proposed guidelines, since these fellows surely have the experience to justify the appropriate mash regimen. Worst case, you might end up with a slightly higher gravity wort.