When a petition is filed for the probate of a will, for the determination that a consent of a spouse to a will is a valid and binding consent or for administration, if all the parties interested as heirs, devisees and legatees enter their appearance in writing, duly acknowledged, waive the notice otherwise required and consent to an immediate hearing, a hearing may be held, in the discretion of the court, as if notice had been given. Such entry of appearance, waiver of notice and consent to an immediate hearing may be given by: (a) A trustee on behalf of the trustee and all beneficiaries of the trust; (b) a conservator on behalf of the conservator and all the conservator’s conservatees; (c) a guardian on behalf of the guardian and all the guardian’s wards; (d) a guardian ad litem on behalf of the guardian ad litem and all of those whom the guardian ad litem represents; or (e) by an attorney under the servicemembers civil relief act on behalf of an attorney appointed pursuant to the servicemembers civil relief act and all of those whom such attorney represents.