current_time( 'mysql' ) returns local site time: 2021-02-28 12:39:40
current_time( 'mysql', 1 ) returns GMT: 2021-02-28 01:39:40
current_time( 'timestamp' ) returns local site time: 2021-02-28 23:39:40
current_time( 'timestamp', 1 ) returns GMT: 2021-02-28 12:39:40