135.10. For the purposes of section 135.9, where more than one building is being constructed under any of the circumstances described in that section on one site or on contiguous sites, no undue delay is regarded as occurring in the construction of any such building if construction of at least one such building proceeds after 31 December 1982 without undue delay and continuous construction of all other such buildings proceeds after 31 December 1983 without undue delay.