If each stripe melted in about an hour, about three hours would have passed when three stripes melt.
What type of conditional is it? I did not find the type of "If past tense, would have perfect".
It's called mixed conditional.
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Your sentence doesn't come across as correct.
However, the pattern "If past tense, would have p.p" is a mixed conditional.
e.g. If I had enough money, I would have bought that luxury car yesterday.
That implies that you still (at the time of your speech) don't have enough money if even given the chance again.
I interpret it as a zero-conditional (general truth statement) set in the past, followed by a conditional future perfect. It is not an unreal condition.