My first century was actually 104 miles and it took me 9 hours total - 7 hours 40 minutes on bike. The middle part is a really big climb, so that slowed me down quite a bit. We stopped four times, including a lunch stop. This wasn't an organized century.

My second century was 109 miles and took 7 hours with 6 hours 20 minutes on bike time. It was less climbing - mostly rollers - and organized so there were lots of riders around to keep me motivated and moving faster.

So, it all depends on the amount of climbing, how many stops, and your general pace.