What are the limitations of time dependent workflow in Salesforce?

DATE or DATETIME fields containing automatically derived functions, such as TODAY or NOW.
Formula fields that include related-object merge fields.
You can’t add or remove time triggers if:
The workflow rule is active.
The workflow rule is deactivated but has pending actions in the queue.
The workflow rule evaluation criteria is set to Evaluate the rule when a record is: created, and every time it’s edited.
The workflow rule is included in a package.