Minecraft wiki entry for weather, associated text: Must be a 32-bit integer number. Must be between 0 and 1999999999 (inclusive).
Specifies the time in seconds for the specified weather to last. If not specified, the duration defaults to 5 minutes. If 0, resets to random weather duration. The maximum value of 1999999999 seconds is approximately 63.4 years.
In bedrock edition, it is the number of ticks for the specified weather to last.