I have absolutely no idea of a time lapse between idea to execution, only that it wasn't instantaneous.
I doubt that Ney made ANY provision for anything and only took the units he could immediately see on his 'ride.' He had a very bad habit of doing that throughout his career.
The Austrian cavalry didn't have a tradition of acting in mass which may explain that one; the Prussians didn't use a cavalry reserve. For the Russians I'll take a look in Zhmodikov as they did deploy large numbers of horse (for example, there was an 'advance' of a large number of Russian cavalry on the French left flank at Eylau that was defeated by the French light horse in the cavalry screen there-it's in Parquin by the way).
We might also want to define 'mass.' Two regiments can be 'massed cavalry' just as two artillery batteries/companies can be said to be 'massed.'
One battle from both sides that might be interesting in this respect would be Leipzig as there was a large amount of cavalry action in the center on the first day. That's when Latour-Maubourg had his leg blown off.
What do you think?