I have not tried to ride a century completely cold but for commuting. I rode a century w/ a buttload of climbing last ... July? I went from commuting 70 miles a week to adding a 30-50 mile ride on weekends, and then tried to get in rides of 60-70 miles in the last couple weekends before the big day, which was a Sunday, followed by another 70 mile commute week. I believe I did no more recreational riding until the last week of September and then I did another century cold-esque except for the May-July century practice plus commuting year-round. That 2nd time was a bunch less climbing and much easier despite no additional riding beyond commuting.

I am planning a couple more century rides this summer but at this point I mostly just want to ride on weekends so I am not holding back, I did 40 last weekend, will aim for that this weekend, might do 50-60 the following, after that I don't know except I don't think I will try century rides until August or September so I may have slacked off my weekend rides by then.