Maybe I've found the source of misunderstanding. When you say in English *Yesterday I ate at 2 pm*, does it mean that at 2 pm you have already eaten?

No. It means that the eating occurred at 2 pm, but doesn't say anything about when eating was completed. Without any further context, one would assume that the eating started at 2 pm, but it's not literally saying that. You're taking your finger, pointing at 2 pm, and saying that that is when you ate. You're not discussing how long it took you to eat it or when you started or stopped eating. 2 pm is treated like a durationless point in which the action occurred, even if the action is not literally instantaneous.

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SuStel
http://trimboli.name