place the WeatherCycle.asi and WeatherCycle.ini inside rdr2 directory.

open WeatherCycle.ini and follow this:

Add '*' after the time to select a weather type. For example: Set Clear Time = 30* it sets the clear weather type. 30 means Real 30 Minutes. Select Multiple weathers by adding more asterisk(**...***...); like this: Set Rain Time = 1** it means second weather for 1 minute in your cycle.

Create your Custom Weather cycle using this method: 

Set Clear Time = 100*
Set Cloudy Time = 10**
Set Rain Time = 12***