By default, the date and timepicker in GD follows the 12-hour notation, wherein it goes from 0-12 pm and 0-12 am. You can, however, change it to 24-hour notation with the help of a simple code snippet. 

Don’t forget to also change your WP settings to 24hr time in WP Admin – Settings – General

Changing Date and Time Notation

Use the following code snippet to change the date and time notation to 24-hour model: 

/**
 * Event times 24hr timepicker.
 */
function gd_snippet_event_times_24hr( $attrs = array() ) {
	$attrs['data-alt-format'] = 'H:i';
	$attrs['data-time_24hr'] = 'true';

	return $attrs;
}
add_filter( 'geodir_event_aui_start_end_time_attrs', 'gd_snippet_event_times_24hr', 11, 1 );

/**
 * Business Hours: Use 24 hour time format in time picker.
 */
function gd_snippet_business_hours_24hr_params( $params ) {
	$params['time_24hr'] = true;
	return $params;
}
add_filter( 'ayecode_ui_calendar_params', 'gd_snippet_business_hours_24hr_params', 11, 1 );

function gd_snippet_business_hours_24hr_format( $time_format ) {
	return "H:i";
}
add_filter( 'geodir_business_hours_input_time_format', 'gd_snippet_business_hours_24hr_format', 11, 1 );

Furthermore, if you wish to change text strings and further customize or localize GD, you should consider going through our guide to translating or localizing GeoDirectory.