I'll probably get some flack for telling you this, but there is absolutely zero difference between the whiskey at the top of the bottle, and all the rest of the whiskey in the bottle. If that were the case, then why not just shake the bottle up for a while before you open it? I'm convinced that the term "neck pour" was devised as some kind of cruel joke by those who know better, and are trying to make new whiskey drinkers believe it so they can laugh at us. Removing the cork, pouring a little out, and letting a little air in will not do anything to the rest of the whiskey in the bottle over a short period of time.
If you don't believe me, then analyze the process of distilling, aging and bottling spirits. Throughout the entire process, there is always air in contact with the whiskey. All the years that it is aging, air is continuously entering and leaving the barrels. When the barrels are dumped, the spirit is exposed to a lot of air. When barrels are blended, they are exposed to air. Do you really think letting in a small amount of air for a few days, or even a few weeks is going to change the taste of a whiskey that is 2-10 or more years old? If that were really the case, then once the master distiller has tasted from a barrel, and determined that it has reached the point in it's aging where it is just perfect, then don't you think they would take great care to insure that it doesn't further mix with the air prior to bottling?
So no, the little bit of air that goes into the bottle when you first open it is not going to make the whiskey taste materially different next week than it does this week. What does change is your perception of the spirit. The parameters and variables that encompass your drinking experience will change. You consumed different foods and drinks on each of the days. This will change how things taste. You may be drinking at a different time of day. Your health or your state of mind could be different. All these things can impact your perception of what you are drinking.
What will happen over time is that water, alcohol and other volatiles may evaporate from the bottle. And eventually, the taste of the whiskey could change, and may actually get worse. Especially over long periods of time and after the bottle is more than half empty. Many whiskey drinkers will take a particularly special, high dollar whiskey, one that they may want to keep for a year or more after opening, and pour it from the original bottle into a smaller bottle after drinking it down past the halfway point. To some degree, this will lessen the amount of empty space in the bottle for evaporation to take place. But these changes happen over many months or years. Not days or weeks.
I was a noob myself a few years ago. And I heard people write and talk about neck pours. So I did the research, and I spoke to some whiskey experts. Every one that I trust told me there is no such thing. And common sense tells me the same.