Because occasionally it is that one time when ____ planet is switching from sign to sign like Capricorn to Aquarius or what ever. For most of the planets, especially the outer ones; it is not often at all. But what if you are the person who is born a few minutes before or after it switches. It's gotta be someone.
I am more talking about the moon sign particularly because that changes every few days. My moon sign would be different if I were born a few hours later. Mercury, Venus, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto, no. Those don't move a lot. But they do move some time.
That's not what I was really trying to get across when I emphasized time, though. Typo. I meant houses. The houses which the planets are in definitely change multiple times a day. Houses!