I finally got an official answer from Microsoft. The Calendar Search feature in OWA is only available in Exchange Online:
According to my knowledge and confirmation with product team, the feature is only available in Exchange Online. Currently, we havent receive any announcement about when this feature will be available
in Exchange 2013.
I will send feedback to our product team about your need with this feature. And I will keep you updated when this feature is available in Exchange 2013.
If anything is unclear, please feel free to let me know.
Have a nice day!
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Best regards,
Yang Yu
Microsoft Partner Support Community Technical Support Engineer
Microsoft Global Partner Services
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Marked as answer by
Kevin Pomerleau1
Friday, May 15, 2015 1:21 PM