Relative start times (> 1 month) in the Data Browser not handled correctly by start/end time dialog box

[skyfrench]

Relative start times > 1 month set by the start/end time dialog box are converted into days for display in the 'Start Time:' text edit. When the start/end time dialog box is re-opened, the time is displayed incorrectly because the day spinner takes a maximum value of 31.

e.g. to reproduce:

• Open a Data Browser plot
• Open the dialog [...]
• Set a relative start time of 1 year
• Accept the change; 365 days is displayed
• Re-open the time dialog
• The relative start is shown as 31 days in the spinner boxes, but 365 days in the start time test field