Steps to reproduce:

1. Create graph widget
2. Add Data set
3. Select "Time period" tab and select some period
4. Save graph widget (time period icon isn't visible)
5. Save dashboard (time period icon is visible)
6. Edit dashboard (time period icon is visible)
7. Edit widget and close modal window by clickin on close icon (time period icon is still visible)
8. Edit widget and press Cancel or Apply button (time period icon isn't visible)

Result:
Time period icon is visible in dashboard edit mode
Expected:
If compare with older zabbix versions - time period icon is visible only in dashboard view mode (6th and 7th steps are not correct behaviour)