Original question

I wonder if there is a way how to fix (make constant) specific Time Zero for specific workflow. I mean only time. The day would be same as system date.

Solution

You can define a cardinal timestep for this particular workflow in the workflowdescriptors.  For example something like this:

    <workflowDescriptor id="xxx" forecast="false" visible="true">
        <cardinalTimeStep unit="hour" multiplier="6"/>
    </workflowDescriptor>

Another option would be to define the times at which the simulation should run explicitly.

	<workflowDescriptor id="xxx" name="xxx" autoApprove="true" forecast="true" visible="true">
		<cardinalTimeStep times="01:00 07:00 13:00 19:00"/>
	</workflowDescriptor>

NOTE. After setting the cardinal time step it is not possible to run the workflow at time steps other than what has been specified. If you'd still like to be able to, make another workflow e.g. xxx_manual_T0 which would be a copy of the initial workflow, but then do not set the cardinal time step in the workflowDescriptors.

	<workflowDescriptor id="xxx_manual_T0" name="xxx_manual_T0" autoApprove="true" forecast="true" visible="true">
	</workflowDescriptor>