As you suggested in question 1, master pages would be the most efficient way. If you know the location of Blurb's magenta trim lines, it will be easy to put your own trim lines in the right place because InDesign can help you with the math. Simply draw your time line, select it, and in the Options bar, add or subtract the distance you need. You can type a - to subtract and a + to add. When you hit Enter/Return, your trim line will move to the right position.
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