I suppose with night time temperatures it's best to go for the lowest
figure, so that people organising barbecues, etc, are prepared.
A noticeable plunge in temperature in a rural area (Sparsholt, Hants)
on Sunday evening, I'd guess down to about 15C by 10.30pm. The past 10
days or so have been characterised by warm days but often rather cool
nights, unusually for this time of year.

Nick