It is not acceptable to the Lord for anyone to be unfaithful, whether such a person is being watched or not. A Christian who is not faithful does not belong to the Lord because if he or she is, then he or she would know that the Lord is, then he or she would know that the Lord sees everything. Nothing can be hidden from the Lord.
Who then is a faithful and wise servant, whom his lord hath made ruler over his household, to give them meat in due season? Blessed is that servant, whom his lord when he cometh shall find so doing. (Matthew 24:45-46|KJV)
If unfaithfulness is found in anyone, it is a sin to be repented of and forsaken. Every day should be a day to be faithful.
God will reward everyone for what is done on earth, not just a particular time or day. Hence, it pays to be faithful in all things at all time.