SafeValue debe usar [propiedad] = vinculante:

constructor(private domSanitizer:DomSanitizer) {
  this.massTimingsHtml = this.getInnerHTMLValue();
}
getInnerHTMLValue(){
  return this.domSanitizer.bypassSecurityTrustHtml(this.parishDetail.mass_timings);
}
Tense Tortoise