SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'b51015f64435fd00230b3be8d173c1f87b5eed6a38872152f9bb6011f4a8c589' 
  AND token = 'KG/DPE4IqAAhNVbs+ffLKMKmEIvS9vIqX/grsXUzns0=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00036

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "message": "Impossible WHERE noticed after reading const tables"
    }
  }
}