> I stumbled upon "on the spur of the moment" in wiktionary.com and
> found that the meaning given is "on very short notice". The
[quoted text clipped - 6 lines]
> decision on the spur of the moment and have regretted it ever
> since".
My own view coincides with yours, but the OED (1989) allows for
both:
d. /on (or upon) the spur of the moment (or occasion, etc.)/,
without premeditation or deliberation; on a momentary impulse;
impromptu, suddenly, instantly.

Signature
Noel