I haven't had DMS problems, but for lighter beers, I mash for 90 minutes and boil a full 90. I then immersion chill to about 55, then to the fermentation chamber to chill down the rest of the way for lagers (45F or so); ales get pitched around 55. It takes almost a full hour for me to chill down a 10 gallon batch from boil to 55, using my well water (thankfully, the well water is cold), but I am below 70 degrees within 20 minutes.