Even after a bit of digging, have not found a way to change the increment. BTW, the increment is by 1 minute or hour depending upon where the cursor is placed. The increment/decrement works regardless if the spin button is present or not. Just use the arrow up/down keys.
Only thought at this time is by creating your own macro.
Sorry for delay but turned out to be unexpectedly busy today.
Have found a way to do in a macro with some push buttons. Agree with @jimk abut lack of knowing which button is pressed.
There are methods in the controls view for up() and down(). The additional problem here is as I mentioned, depending upon where the cursor is as to whether the hours or minutes is affected. So that can be done by setting the selection. You can use two push buttons - one for up & one for down (adjusting by 15 or whatever you want). The spin buttons can be left in the time control if you want single adjustments.
Both push buttons call the same macro. Used
Execute action event. The name is checked to see what function to apply.
Dim oForm As Object
Dim oDocCtl As Object
Dim oField As Object
Dim oCtlView As Object
Dim x As Integer
Dim oSelection As New com.sun.star.awt.Selection
oForm = ThisComponent.Drawpage.Forms.getByName("Form")
oDocCtl = ThisComponent.getCurrentController()
oField = oForm.getByName("TimeField1")
oCtlView = oDocCtl.GetControl(oField)
oSelection.Min = 0
Rem Setting Max to 1 or 2 places it in the hours portion
oSelection.Max = 4
oCtlView.Selection = oSelection
If oEvent.Source.Model.Name = "PBdown" Then
For x = 1 to 15
For x = 1 to 15
Of course, change names of form, control and push button (my other for test was PBup) to fit your needs.