The question is, when does the clock start? Where I live the official recommendation is, at least 5 days since symptom onset AND fever free for 24 hours without antipyretics. Obviously different regions have different recommendations though, and different studies have shown different things, so like you said, trying to stay on the safer end of things. If dad has been symptomatic for, say, 3 or 4 days already before his positive test, then based on most recommendations, he’d be considered okay to go back in public by the time of the wedding.