Xero has resolved this issue

Please note that some customers are unable to log into Xero. We are seeing intermittent issues. Further information and updates regarding logging in issues at https://status.xero.com/

The latency is back down, Xero is continuing to monitor the situation.
https://status.developer.xero.com/

Xero has identified that they are having performance issues on the API this is causing latency and slow response times. Further information and updates https://status.developer.xero.com/