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.