Clause 13.5 only talks about the period of reply being extended, not a timescale already written within the contract. Therefore only something where the response time defaults to the period of reply (e.g. acceptance of design or a subcontractor), or under clause 62.5 the period to respond to a quotation can be extended. Everything else is "locked in" to use your language.
My bigger question is why should they ever need longer than two weeks to respond to a programme - especially when it is only another two weeks when the next one is due anyway. They should be able to respond to a programme within two weeks, especially if the programme is well presented with a thorough narrative attached explaining exactly what it shows and what has changed.
My bigger question is why should they ever need longer than two weeks to respond to a programme - especially when it is only another two weeks when the next one is due anyway. They should be able to respond to a programme within two weeks, especially if the programme is well presented with a thorough narrative attached explaining exactly what it shows and what has changed.