All the examples that you used, are using exaggeration to add emphasis. They are exaggerating a small amount of time to emphasize how quickly something is, because it is relevant for the rest of the sentence. Let's go step by step. First of all, whenever you hear "about" followed by a quantity, it often means "almost" that quantity. The decision to say "about" varies with context. Consider the following: You are invited to a friend's house, and you are offered some cookies and milk. You already have the cookies in front of you, and when they ask you how much milk would you like to drink, you politely answer "About one glass". In this kind of context, saying "about one glass" means "just a little less than one full glass" or "almost one full glass", but definitely not "full glass". In this manner, it could be used to be polite or modest. Suppose you are offering tea to your guests, but it isn't hot enough yet, you will tell them that the tea will be ready in "about a minute", because "one full minute" would be too much. In the phrases that you are analyzing, your understanding is correct, and the specific amount of seconds is almost irrelevant. Take for example: "It took me about two seconds after I unwrapped it to think this is a placebo". You are correct to understand that what this person meant is "I knew right away". The reason why that person said "about two seconds" instead of "right away" or "immediately" was his or her personal choice of words to emphasize just how quick he or she knew something. From the rest of the sentence "...to know it was a placebo", it appears that the general idea is one of deception. Without more information, I infer that the person is disappointed in the appearance or presentation of something he recently unwrapped. By "how quick" he or she realized the sad truth, he or she emphasizes the disappointment, based on a previously conceived idea that if a knock-off was of better or superior quality it would deceive in a better fashion, and the person would take longer to realize the truth.

1. Yes, they basically mean the same thing. 2. You can think of it that way, but it is not very natural for English speakers to do so. (more on this below) 3. 'A while' can refer to many different lengths of time, so if 5 seconds is considered a long time, then yes you say that it took a while. On this subject though, it is not very common to say it "it took me 4 seconds to do this" or "he realized it after 2 seconds". Most of the time we'll just say "it took a few seconds" or "he realized it after a couple of seconds". It depends on the situation, but most of the time the specific number does not matter in English, and people will think you are strange if you are too specific. If it is a situation when the time is actually important, like "He ran the race in 12 seconds" or "This experiment lasted 7 seconds" then it is necessary to be specific.

No, they are not the same. 1. It took me (all of) two seconds before..... This means he did not get it right away. He had to think for a very short while. 2. It didn't (even) take me a second to realise..... This means he got it right away. The time required to think about it was negligible.