The zone has to be in a blizzard for him to appear. The easiest way to set this up is zone in/out of Feywood until you get a blizzard. Once you get a blizzard weather effect go to the zone Silverflow's End but do not cross any frozen or broken areas, doing so will reset the weather effect.
I did this fight with Vaan (71), Ashe (68) and Penolo (67). It was kinda dicey for awhile and I almost reset. Having ribbons would have made things a whole lot easier. Make sure you have expanded out on the remedy inclusions and have a ton of Chronos with you.
Here's a video of my fight: