I made a batch of braggot (~46% honey) a couple of weeks ago, and used the Duvel strain (a pack of Wyeast 1388 and a vial of WLP570). Pitched at 65 and ramped it up to 82 over the course of 7 days. Is there a good rule of thumb for how long the yeast should sit at the high temperature before I cool it, or is it best to just watch the gravity and wait until the yeast finishes?
If the temperature schedule was intended for high attenuation and cleanup of yeast byproducts, such as diacetyl and acetaldehyde, then you should keep it at the warm temperature until a minimum of two days after terminal gravity has been reached.
If you fermented warm to produce more esters, fusels, and phenols, then you only need to keep the beer at the current temperature until terminal gravity is reached. Dropping it earlier will cause the yeast to slow, or even exhibit heat shock, and your fermentation may fall a point or two short of the lowest possible final gravity.
Also, just a warning - you're probably going to have excessive acetaldehyde from fermenting this warm - I would guess upwards of 300 ppm.