The Evohome app lets you override the scheduled target temperature, but only immediately. This recipe lets you set a timer to do this at a point in the future. You can't set this trigger on IFTTT as a one-off, so I have used a trigger that repeats annually. To stop it repeating, you just need to delete the recipe (or change when it is set for) in the 364 days after it has triggered.
Explore more great ways to automate Date & Time and Honeywell evohome