Question?

[hotwine]

Suggest you buy a regular 750 ml of the same wine and decant it for about four hours to see what that does for it. Then sample it evey hour or two to see how it holds up. At whatever point it seems to have peaked, you can use that to guess the point at which the magnum might be ready, assuming the mag would need at least two years longer than the 750.

It's a whole lot of guesswork but fun to experiment.