I'd say it depends on the whisky, both brand and year. And some brands don't seem to change whereas others do.
1) I have had 2 bottles of Laphroaig 15 now that tasted better after 1 or 2 drams, that is: I opened the bottle, had 1-2 drams and then had a third dram after a short time (few days, a week). From the third dram on, Laphroaig 15 is great (it was good with the first 2 drams, but not great).
2) Glenmorangie 10 doesn't change in my expierence, even a year after opening the bottle.
3) I felt my first bottle of Lagavulin 16 changed a lot after emptying by 1/3; it had less smoke. However, this might have been my mood, because the two bottles I had after that didn't change much, if at all.
4) It seemed for me that Macallan Fine Oak 12 improved after I had emptied it by 1/3.
5) And so on....