A slightly different procedure: The Trippel is a very big beer. When I'm doing a very big beer with a sugar addition, I generally add the sugars after a couple of days of fermentation. Two reasons: First, the yeast are going well. I pitched them into oxygenated wort then oxygenated again 12-18 hours later. They've adapted to their environment and have reproduced so you have a lot of yeast cells to do the work. Second, yeast given simple sugars - invert syrup is simple sugars - get lazy and will ferment maltose reluctantly, if at all. By letting them ferment the maltose a couple of days before adding the glucose-fructose mix, you're certain they will ferment completely through the maltose. The key to a good Trippel is attenuation, the procedure I describe will help the beer attenuate out without being too oily in mouthfeel or too sweet. Mix the syrup with its volume of water, boil it ten minutes, cool it and add it two days after fermentation starts to maximize your attenuation. And let the temperature rise on its own after about a two thirds of the sugars have been fermented.