JCT: Right to extension of time due to PM delaying choosing materials , changing scope & quantities of work.

I am currently working on behalf of a small contractor who has taken on works to a public sector venue.
The clients PM/project architect is very lax when it comes to instructions, selection of materials.
We were due to start on ceramic floor tiling to a substantial area, when it became apparent that tiles that we were to only make isolated replacements were all boast.
It was decided by the client to replace these as well which increased the overall area by approx 1/3.
The tiling contractor had advised that the tiles were not fit for purpose.
The client/architect duly had taken the advice and agreed to the variation in tile type. However the PM/Architect has taken one full month to make an alternative selection with several follow ups. (all recorded) Unfortunately the selection has come so late that it has coincided with the manufacturer holiday period in Italy (whom ares upplying the tiles & specials)which is one month. The architect while acknowledging the holiday period is not accepting our application of an extension of time/duration due to delays and material shortages outside our control.
I would welcome guidance as to clauses etc that may be in our favour OR not.
Thanks in advance. (Jct Main Contract with Quantities)

The change in tiles is a Variation and a Variation is Relevant Event for an extension of time (clause 2.29.1).

The Architect is required to grant an extension of time that is ‘fair and reasonable’ (clause 2.28.1) and this would include the 1 month shut down.