SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'e8a51cc685523708f2260a78c61d5eb3edc95f0519096dcae0d763349272a13e' 
  AND token = 'jFv3tBFcGugd+F0eUZpxyIWYnfncT9wVsY5chMYxTlg=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00027

JSON explain

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