Well it shouldn't take any trial and error. Just double-click the model a couple times to open up a middle strand where the text is. You can see exactly where it repeats. Hover your mouse to figure out the correct cut-off time.
Thanks for the tip, but how does that tell us what SPEED value to use?
Using that trick, don't we still have to use trial and error with the speed slider/setting to get it to fit a given duration? And with the fixed integer speed values, it's often not possible to hit the cut-off exactly.
(BTW, what am I supposed to see when I hover over the area you pointed to? Is there supposed to be a tool-tip popup? Is there a setting for that? I'm not seeing it).