Wait till Friday afternoon/evening, ride for a half hour to an hour at a very light pace. Keep your cadence high and your legs loose. Check everything on your bike for proper operation. Take the last 2 or 3 minutes and push a little harder, say a few mph faster than your target century pace. Eat a carb-laden meal within 30 minutes of getting off of the bike. Recheck your stuff and go to bed. Be confident that you've done good work up till now and remember to ride your own pace.
EDIT: Start yor prehydrating on Thursday, though.