Hey Jason,
I think the answer depends upon the audience you're trying to serve. Many organizations remain open for extended hours in order to reach young professionals otherwise not very available during the work week. In my experience, this is why/when a museum will have a night or two open that often is specifically marketed to young professionals or with public programs geared toward them.
Extended hours can also be helpful for working parents, if they're looking for things to do locally after work hours. However, if the majority of your audience is non-local folks on vacation, then extended hours may not benefit that audience as much. If you're looking to target a new or local audience, then perhaps this would be the right approach, in combination with marking and programs geared toward those audiences.
Do you have a sense of who you're trying to reach with the extended hours?
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Chris Green
Director of Collections & Exhibits
Pacific Grove Museum of Natural History
Pacific Grove CA
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