It seems to me that より has virtually no meaning when used as shown below.
Consider these:
Please come before five O'clock:
五時前に来てください
五時より前に来てください
Please come after five O'clock:
五時後に来てください (*ungrammatical as observed by sawa)
五時より後に来てください
(Question) What does より add to the sentence? What additional nuance is there? And why is omission of より acceptable for 五時前 but not 五時後?