I don't know what kind of shape you're in, but 155 miles is a hell of a long day's ride, especially for a first attempt. You won't be carrying much of anything, so you should be able to make pretty good time, but i think 9 hours might be rather over-optimistic. I'd say you'd be doing well if you were on your bike for only 12 hours, not counting breakfast, lunch, dinner & breaks time. If you're set on doing it in a day, i'd suggest leaving a couple of hours before dawn and expect to arrive well after dusk. I'm not trying to disuade you, because
it is do-able; I've done over 200 in a day with loaded panniers, but that was in a 24 hour period when I was a lot younger. if you are into athletic challenges, I'd say go for it.
On the other hand, you might actually enjoy it a lot more if you were to do it over two days.
in addition to JN's advice on what to bring, I would suggest not only studying maps, but to bring them along. cities can be tricky to navigate at times, and roads can be closed. a basic first aid kit would be prudent, and some high-energy tunes can help keep you motivated.
have a good ride!
