My recipe calls for a 4 to 5 week secondary fermentation, which falls on Christmas when I will not be around. It also calls for pitching additional yeast 3 days before kegging.
Should I keg the beer at 3 weeks or go to almost 6?
What is your OG and projected FG, also how much yeast did you pitch? I find that high gravity beers at or above 1E6 cells/(ml*degree plato) can finish fairly fast given the right temperatures. If you are worried about overpressure in your keg after only three weeks of fermentation - as I would be with bottles - you can always build or buy a spunding valve .
As an aside, most people nowadays skip secondary fermentation, especially when kegging. There has been limited to no evidence of benefits of separating yeast from beer for a secondary fermentation on a homebrewer scale. One of Marschall Scott's early xbmts was on this if you want a read