SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '7c21bfe4e577e00ea795ed016cd96ca33dc574b967da172794e3a06658965390' 
  AND token = 'u2bMpV6jiH/+HI4CsQsncPSVywGqchj7kKYjnjZJdZs=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00035

JSON explain

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