Why does it seem like guy waits to reply at a certain time?

One time my crush responded to my text after a week while we were in the same class, so I looked at him, and I saw he was staring at his screen (he sits across from me) and I just saw him staring at his email. So, I messaged him, and he was still looking. It was like he was planning on when to text me. He randomly ignores my texts sometimes but looks at me in class secretly. Did he notice me more often or something (this is just something I'm wondering... I ask a lot of questions but I'm curious)? And why just not reply but look at me in class? Am I just overthinking?
Why does it seem like guy waits to reply at a certain time?
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