I already answered your question in the support ticket that you opened. For your convenience, I give you the information here as well:
Basically, the events with duration do not respect the MinWidth value and there is no easy way to change this. The reason for that is because these events have start and end DateTime, which correspond to specific points on the timeline. In case you apply MinWidth to these items, at certain zoom levels, items with duration 2 days, will appear the same width as items with duration 1 day. Additionally, the end of the bar will not represent the correct DateTime value on the timeline.
In case I understand you correctly, you actually want only the bullet to be always fully visible and not have a MinWidth value. If this is the case, you could try to implement a fix, using XAML - try wrapping the XAML for the bullet in a CANVAS.
All the best,
the Telerik team