One thing that helps is don't put a tight time limit on it. The 16.5 hours is doable if you're in good shape, the course isn't super hilly or windy, you don't fool around long at stops, etc. But a lot of us have done plenty of rides that went slower than that, too. (Typically, 20 hours for a 400k, for example.) Anyway, extra pressure can suck all the fun out of an event.
I'd say the rest is half mental, half pacing. If you finish a century and still feel fine, I'd say you're in a good position for this.
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"be careful this rando stuff is addictive and dan's the 'pusher'."