How quickly can a guy decide if he is attracted to you/likes you?

After meeting a girl for the first time/being introduced, how soon can a guy decide if he likes you/finds you attractive?

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I was introduced to several new people today at a church. It was very nice, and went on naturally... I would say something like "hey, I'm melanie" then they'd respond with "hey, I'm ___" (and vice versa).

However, I was introduced to this one guy who looked at me for more than a few seconds without saying anything, like a random pause, then said hey... etc

Am I overthinking this? He could just be anxious, right?

I did think he was cute, and wouldn't mind getting to know him better, but I don
How quickly can a guy decide if he is attracted to you/likes you?
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