I've noticed you have already opened a support ticket with the almost the same question and we have already answered you there. So I'll copy the answer here and will ask you to continue the conversation here in order to be available to the community.
You can control the whole Width of the TimeRuler using the MinTimeRulerExtent property of TimelineViewDefinition. You will need to modify it whenever a day has been added in the VisibleDays number. For more details please check the following article from our online help documentation:
However as I'm not completely sure if this is what you want to achieve, so if this doesn't help I'll kindly ask you to share some more details about the exact scenario.
Hope this helps.
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