SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '6b3d456f784d95be950dded155d304afa67b8208b284c8fdc2e6618717a51f12' 
  AND token = '5PQsgXsZm6/rzGRKzNx8u/MiSziPh9TR2VraEyisFyw=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00023

JSON explain

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