The sign is clear but the timings aren't IMO.
OP, your customer is no David Bailey. The No Left Turn sign lower panel is out of focus. Does it state word for word what's on the middle and lower panels of the main signs?
Have you looked at the council's video? It shows you moving at the junction presumably having stopped previously. You are close to the nearside kerb and the left-hand sign would be invisible unless your car is LHD. The question is then how visible and readable is the sign on the right. I suspect it's not clear. These signs are for head-on traffic primarily IMO. From your direction they have placed a No Left Turn sign. Does this convey exactly the same restriction as the main signs?
This is the prescribed sign, Item 2 Part 2
https://www.legislation.gov.uk/uksi/2016/362/schedule/8The sign must convey what's in the TMO.
The sign may not indicate 'term time only' in the middle panel, the permitted variants are specified in the regs.
If it says Mon-Fri 2-4pm for example, then these MUST be the restricted times.
So IMO:
Either the TMO supports the hours given without exception, or it doesn't.
If yes, then the street is restricted for those hours irrespective of school days. If the authority chooses to not enforce during certain periods then I don't know whether this is grounds for appeal, it's certainly the basis for a complaint to the council.
If not, then the sign is improper and fails the LATOR test IMO.