I loved this route!! Was going to take it easy as Will and I had just run the Routeburn Track 2 days before, but after checking Strava and seeing the fastest Women's time, decided it was reasonable to try to do it quicker. The techy flat section at the start keeps you on your toes (I tripped several times), then up the valley is fun yet challenging to even tell where the "trail" is through the scree and boulders, then the slabs at the top are a lung-bursting blast - be sure you have good grippy shoes (apparently there have been multiple deaths on this route)! And the view at the top!!
I arrived at the summit in 53 minutes, faster than the women's record by 5 minutes, but my GPS drift is irritating and shows I didn't arrive until 59 minutes (and also has an odd jump off track and back), but at least that doesn't affect the total roundtrip time.
Highly recommend this route! More info: Gertrude Saddle: the best day hike in Fiordland