40 miles sounds so much better than 37, right?
As you can see from my ride on Saturay, I rode 59.58 miles. Not 60 miles.
I'm pretty sure I will still be prepared for Rev3 Knoxville in 7 weeks even though I didn't hit 60 miles.
When I swim or bike (and run), I stop when my workout when the main set is over and I cool down - that's when I am done.
Furthermore, if a proper warm-up, good economy, great skills, smart execution, great fueling/hydrating and excellent recovery habits are not enforced, the workout stress is not well-tolerated (and consistent training may be difficult to achieve).