UPDATE multiple fields under same condition (IF or CASE)

Need some help. There are some questions and answers here about this topic but didn't found one that fits my need.

I have these two queries:

UPDATE leilaov
   SET seconds = CASE
      WHEN (mesini = MONTH(NOW()) AND diaini = DAYOFMONTH(NOW()) AND horaini = HOUR(NOW()) AND minutoini <= MINUTE(NOW())) 
        OR (mesini = MONTH(NOW()) AND diaini < DAYOFMONTH(NOW())) 
        OR (mesini = MONTH(NOW()) AND diaini = DAYOFMONTH(NOW()) AND horaini < HOUR(NOW()))
        OR (mesini < MONTH(NOW())) THEN seconds-1
   END
WHERE numero12345 = 1


UPDATE leilaov
   SET seconds = IF((mesini = MONTH(NOW()) AND diaini = DAYOFMONTH(NOW()) AND horaini = HOUR(NOW()) AND minutoini <= MINUTE(NOW())) 
                OR (mesini = MONTH(NOW()) AND diaini < DAYOFMONTH(NOW())) 
                OR (mesini = MONTH(NOW()) AND diaini = DAYOFMONTH(NOW()) AND horaini < HOUR(NOW()))
                OR (mesini < MONTH(NOW())), seconds-1, seconds)
WHERE numero12345 = 1

Both work fine and there are no significant differences in execution time. The problem is that I need to update several fields and not just only one.

Whats the syntax to update several fields? Do I have to repeat the condition to each field?

Should I use CASE or IF? Or is there another better option?

Thanks in advance.