SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '138fb516604a95834e2f3d9052d842121fe9789231e5bba6af21576a4f959b35' 
  AND token = '4CoF0jgrIAGAuKh1Qhw2bMveEJWNw2Puh44/5qcXD5M=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00037

JSON explain

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