Kokua Line: Was park guard wrong to make us leave at 6 p.m.?

Question: My wife and I were surprised to be informed by the security guard at Koko Crater Botanical Garden that the park closes at 6 o’clock and not dusk as the sign says. Pretty sure dusk is after sunset, and the sunset was at about 6:30 p.m. that day. The guard said the person he took over from told him that 6 o’clock is the closing time, and he questioned what time is dusk.