Mine so far is 5 days and 4 hours, fingers crossed. May be the network upgrade they have done has cured the problem. I will monitor it for few days.
While ago I contacted draytek support, they said first try to reset the router to factory default, then call your ISP if that didn't work and is possible that the router is faulty. My next step would be to put back the O2 router and record your stats as they will ask u when u call them.