How long does it take to break down glucose, via glycolysis-citric acid cycle-terminal oxidation?

Answer

Best,

Very specifically: how long does it take for an individual glucose molecule to go from the first step of glycolysis (hexokinase) to the last step of the citric acid cycle (in which the energy in the bonds is then actually converted into reducing equivalents for the electron transport chain and oxidative phosphorylation): very, very fast. If you consider that an average enzyme converts several hundred to millions of molecules per second and that about 20 enzymes are involved in the process.

However, this is a very simplistic view of this process, since everything also depends on the concentrations of the products, in which kind of cells the process takes place (for example, muscle cells or brain cells have a very fast metabolism, while cells in the skin, for example, get by with a little less.)
On the other hand, it is also possible that cells do not use glucose at all, but actually create it (eg if you have a sugar dip, liver cells will reverse the whole process and produce glucose from energy reserves). It is a highly regulated process and the speed through the pathway can therefore vary from very fast to nothing to vice versa.

In short: it depends on the circumstances, but if you are referring purely to the enzymatic reactions, without regard to regulations and conditions, I would say, certainly no more than a few seconds.

Well, I hope this made it a bit clearer.
Regards
Leander