1° per day
Sun
An hour of error moves it 2.5 arcminutes. Your Sun sign is safe even if nobody remembers the time.
Your big three
Sun, Moon and rising sign from one birth date — each one labelled with how much your birth time is deciding it, because the three could not differ more on that point.
The reason the three behave differently
One number explains everything
The big three are singled out as a set, but they do not deserve equal confidence, because they move at speeds that differ by a factor of 360. Every argument about conflicting chart readings comes back to this table.
13.2° per day
Moon
An hour costs half a degree. Only matters if you were born near a sign change — and then it decides it.
15° per hour
Ascendant
An hour of error is half a sign. Two hours is a different sign with a different ruling planet.
Reading them against each other
The productive way to use a big three is to look for the contradiction, not the theme. A chart where all three agree is telling you very little — it is one message repeated three times. A chart where the Sun wants recognition, the Moon wants to be left alone and the ascendant reads as easy-going is describing a specific, recognisable friction, and that friction is the only part of the exercise with any use in it.
Which is also why the confidence labels matter. If your ascendant is a coin-flip between two signs, do not build a reading on the tension between it and your Moon. Fix the birth time first, or work with the two placements you can actually rely on.