How do i change the column time format in fullcalendar?

You can use axisFormat: 'HH:mm' to accomplish this. Let me know if this helps.

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Just to complement: in version 2.4.0 this method was renamed to slotLabelFormat.

I use FullCalender V4.2.0 this work for me:

        slotLabelFormat: [
        {
            hour: '2-digit',
            minute: '2-digit',
            hour12:false
        }
        ],