Measure time in ONLY HOUR format

Welcome to WPSE.

You can try to filter it with:

add_filter( 'human_time_diff', 'wpse_hourly_human_time_diff', 10, 4 );

where the filter’s callback is e.g.

/**
 * Human time difference in hours only.
 *
 * @param string $since The difference in human readable text.
 * @param int    $diff  The difference in seconds.
 * @param int    $from  Unix timestamp from which the difference begins.
 * @param int    $to    Unix timestamp to end the time difference.
 */
function wpse_hourly_human_time_diff( $since, $diff, $from, $to ){
    return round( $diff / HOUR_IN_SECONDS, 1 );
} 

but you will need to control where you want to apply this filter with:

remove_filter( 'human_time_diff', 'wpse_hourly_human_time_diff', 10 );

and further restrictions.

Hope you can adjust to your needs.