Is the "at issue date" the same as the "Action commenced"? Or is it 21 days after the action is commenced?

At issue is not the same as the commenced date and likely not 21 days after commencement.  Rule 16 defines at issue as:  case shall be deemed at issue at such time as all parties have been served and all pleadings permitted by C.R.C.P. 7 have been filed or defaults or dismissals have been entered against all non-appearing parties, or at such other time as the court may direct. This is often times a difficult date to determine.    If you are involved in civil litigation I recommend that you contact an attorney to review your case and consider hiring help.    Good Luck!