You're gonna love it.
my first few trips, I didn't use or need a phone. Bars are happy to call you a driver. Although, once i had a phone (used a loner a couple times, then bought a cheapo JA cell) I appreciated the freedom it allows. Meaning, you're not *obligated* to use what ever driver the establishment you're at uses.
As others have said, plenty of time to hit the hilo but you could also go to megamart in mobay. I actually prefer this because once I get to negril, I'm already mellowed after the ride, vibes and sweet air.

Either way, i suggest doing it day of arrival, so you can totally unwind the next day. As Smith said, do not plan anything your first day. Wake up, crack a red stripe and walk out to the beach, sit in a chair, marvel at the beauty and let it all melt away.

And dont forget to come back and write us a trip report. We all love hearing about people's first Negril experience.