I had a look at some standards (such as IEC 62305 & IEC 62561 Standards for Lightning Protection) on how lightning rods should be constructed, and also searched the internet. I found no real answers to this question, including Google and Stackexchange. There are of course some "suggestions", but none of them say this as a "rule".
I live in Germany, and in Germany, the responsible body for this work is "VDE Verband der Elektrotechnik Elektronik Informationstechnik e.V. Ausschuss für Blitzschutz und Blitzforschung (ABB.)" A useful official resource is available on their website.
Of course, in weather like this, I also think it's not a good idea, and as an electrical engineer, I want to protect my colleagues on my team. I can't do anything at the moment other than recommending to the top managers of my company that such installations be done during sunny weather.
Is there a rule or prohibition on when lightning rods may be installed?