The mediation proceedings with respect to a particular dispute shall be deemed to have commenced—

   (a)  where there is an existing agreement between the parties to settle the dispute through mediation, the date on which a party or parties receives notice from the party initiating the mediation, to refer such dispute to mediation; or

   (b)  in other cases—

   (i)  where the parties have agreed to appoint a mediator of their choice for mediation and settlement of disputes between them on the date the mediator provides his consent to appointment; or

   (ii)  where one of the parties applies to a mediation service provider for settlement of disputes through mediation, the date of appointment of a mediator.