respectfully, a different oppinion with experience. 
i kept my son out for.the same reason. had to leave early to pick him up. he could have taken the tests later, but i used him as an excuse to pull my weight with a logical reason and let my sis know that their decission to plan this wedding then made my child stay away. every time i view the wedding pictures i am.reminded that i send mixed messages to my now adult child that weddings are a point of celebration but personal education can be used as a weapon. if i had to do it over again, i would tell him it is inconvenient, their choice, we will be there to see them blessed and celebrate and work together to make sue he gets back on track with a.minimum of time lost. most schools of.elementary ages let students make up tests during recess. 
my son makes.excelleent marks. i have since had to pull him out for emergencies. hes learned to be adaptable and work harder for.priveldges school related in making up . hes learned to be responsible for.his actions. but i cannot get that time back.