SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'db6823ad02f1cdda64c48bf23958338122cc3eedcc0e1f6cebb8e42b35056720' 
  AND token = '42ic8JjehVNvo4CKXxvg2jeGJRRdkbmrojEHSAqd/us=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00017

JSON explain

{
  "query_block": {
    "select_id": 1,
    "message": "no matching row in const table"
  }
}