Rashi D'H Shema [Maybe Paroh's stargazers will say Moshe is "b'dai."]
I always assumed if Egyptian time said 12:00 and really it was 11:58 or 12:02, either way it would look like Moshe is "b'dai." Even if the first born died, but "it wasn't 12:00!". But Rashi only gives one case. If Egyptian time said 12:02 and it was really 12:00, they will say "Chatzos came and nothing happened." He didn't mention, the possibility that the "Makkah" would start earlier than their 12:00 time. Perhaps I was wrong. Once they saw the "Makkah", it would have made little difference a minute earlier or later. But if 12:02 is the real Chatzos, then for 2 minutes while all was calm and well, it would have looked like Moshe was "b'dai." And then 'BANG.' But for two minutes the notion would be conceived that Moshe was "b'dai." And Hash-m wouldn't want them to think, even for 2 minutes, such a thought! Or 2 minutes or 5 seconds. Or perhaps once the thought was in their minds, even the Maakah's arrival couldn't knock the thought out.