Where the will requires an act to be performed by the legatee within a specified time, either as a condition to be fulfilled before the legacy is enjoyed, or as a condition upon the non-fulfilment of which the subject-matter of the bequest is to go over to another person or the bequest is to cease to have effect, the act must be performed within the time specified, unless the performance of it be prevented by fraud, in which case such further time shall be allowed as shall be requisite to make up for the delay caused by such fraud.