This is an idea and explanation of some effects that an inaccurate birth time can cause.
All cycles have their own timing.
An accurate birth time is needed for calculating accurate dates of active and inactive periods during the long lasting cycles, especially when they concern the Ascendant, the Midheaven and the Moon positions of the birth chart. The Ascendant and Midheaven move so quickly that they can be compared to the second hand on a watch. If you have ever watched the moon move across the sky at night, you have noticed that it moves quite a bit in as little as fifteen minutes, especially noticeable when rising or setting. The Rising Sign, or Ascendant, can be off by that distance, in fifteen minutes. The birth pattern is fixed, but the planets keep moving around it day by day at their own rates of speed.