Show cause notice - Is there a time frame to take disciplinary action?

We have given a show cause notice to one of our employees who was found lying down on floor and using mobile phone in his relief time at night shift (not in lunch or tea break). We used to give this relief time for 10 min for employees to get refreshed. He had replied to it. Is there is any time frame to take any disciplinary action or give feedback for his reply.

Why was the Show Cause Notice given?
No offence seems to have been committed.
Your company needs to inform him that matter is closed in writing.