Not able to change time format, for example to 12 hours AP/PM.
GLPI support a lot of languages, but it isn't very flexible in setup language formats, for example change 12/24 hours format.
It would be fine to have a option to change time format at least 12/24 hours. Better would be add option to also use custom time format for displayed time.
For example Wordpress use 4 option and one custom:
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