It uses locale WP option, that’s suits me. Closing the topic
That’s it,
This setting is based on your site language by default, in Settings > General > Site language, choose English (UK) instead of English (United States) for example.
In Booking Activities > Settings > Messages tab, if the “Calendar localization” option is set to “Based on more WP settings (Site Language, Time Format, Week Starts On)”,
go to Settings > General and you can change the “Time Format” option without changing the Site Language.
Dont forget to change the other date and time formats in Booking Activities > Settings > Messages tab too (replace g:i a with H:i).