SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'fd31b3bd08656412f138a7a8b1f2454f880e3942a3f1473051549b3f4a987db0' 
  AND token = '7fbLhT+jWG7YBV7c1pNzOW6wfYzG8y3cQq1oXoDK9gQ=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00041

JSON explain

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