It's possible to customize the options displayed for relative time and the auto-refresh options.
From Dashboard setttings, click the Timepicker tab. From here you can specify the relative and auto refresh intervals. The Timepicker tab settings are saved on a per Dashboard basis.
In Grafana 2.0, it's now possible for individual Panels to override the Dashboard time picker. Please check out the [whats new in 2.0 guide](../guides/whats-new-in-v2/) for further information