Please take look at InfluxDB+Grafana persistence and graphing (Showing diagrams in your openHAB sitemap …as ‘Image’ Element). You have to enter from and to this way:
Image refresh=60000 url=http://monitoring-host:3000/render/dashboard-solo/db/mydashboard?panelId=5&width=700&height=350&from=now-48h&to=now
As an alternative, you can use Webview