SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '51715902b42122e866afa3901e7e8c939062e7fb25089d027b59756a587a67a9' 
  AND token = 'h/17tcHjRkRgIkYcC6pr1Cjy7dyJtOG1bS+IyfIP+ac=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00013

Explain
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE Impossible WHERE noticed after reading const tables