What is the time limit for construction of house to claim exemption u/s 54 or 54F?

To claim exemption under section 54 and 54F construction of a new house property must be completed within 3 years from the date of transfer. Date of commencement of construction is irrelevant. However on the basis of some court decisions , higher judicial authorities does not deny from giving exemption even if the construction of a house property is not completed within 3 years from the date of transfer on the belief that most of the sales consideration have been spent for construction and only some part of it is left.