What's the difference between the month calculated by Feng Shui master and reality?

Feng shui masters generally use the lunar calendar, or rather, not the lunar calendar, but the 24 solar terms.

Basically, the first month in silver moon begins in spring, which is somewhat different from the first month in the lunar calendar.

The first month in silver moon begins in the beginning of spring, usually around February 4th in the solar calendar. So it's about a month away from the solar calendar.