SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'c8735abce567ef3d29a562b58527ce306656761444890af22a6af3ec9c4198ad' 
  AND token = 'RUBNu9YlQzsXXd2LjPP6QUoe+D6IVM/oveJiE5NvPgk=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00018

JSON explain

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