SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'b9c7206829628c4c8f4304ee1856813e8b254adc5ecebf04e17dff09303c38a3' 
  AND token = 'FQqFV4M3tjckEV6ivXybxVM4uVzc151XHYmONVAoxeY=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00043

JSON explain

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