I agree that good attendance at school makes for good results, but if you have a very bright child their success will have little to do with the number of days they spend at school or even whether they are taught in a garden shed. They usually destined to succeed anyway.
With most other, merely average, or less academic children, it has more to do with their wellbeing. This includes happiness as much as formal education, although there's no denying they go hand in hand. High emotional well-being helps all pupils engage in learning, and actually helps them achieve higher academic grades.
So, spending less than two hours out of school for a special event isn't the end of the world, in my view.