SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'a39fbb9b460959f1e61db5ddd55f01ac46b607ac216c2f3c08c0492c941de6b8' 
  AND token = '+t9kTLIgAyZp4azguNoJBDYdRHvHK8WDwtqj/xeEmzg=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00024

JSON explain

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