Only more context can tell us whether the hypothetical taking was imagined as taking place at the time if the not being there: If you had been at home on Tuesday at eight, I would have talked to you on Tuesday at eight. If you had been at home on Tuesday at eight, I would have talked to you the next day.
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hachi8but don't get when exactlyOnly as exactly as the expression "at that time", which is part of the sentence. Presumably the people having the conversation know when "that time" was.