How long I should wait for a response for a coffee date?

So, there is this guy at work. We know each other for about two years now. He is the kind of quite and calm type of guy. Also, a direct person at least when it is related to work stuff.

About a year ago, he showed some signs of interest but the time was not right for me and he did not ask me out.

I asked him if he want to get coffee sometime. He said "umm, yeah" with a smile. I said "this week?" and he responded he has some stuff to take care of this week and it not a good time for him. So, I said ok lemme know then. It is been 4 days and he did not get back to me about the time.

I thought he was interested. Did I a gage his interest for coffee date incorrectly?

Would you suggest asking him again or I should wait?

Also, any suggestions about how I should ask?

How long I should wait for a response for a coffee date?
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