back in nov i spent a week in san juan. i had the same constraints of a hotel in san juan and great diving hours away. i ended up diving two days, one in farjardo and the other in san juan.
the drive from old town to farjardo (did it three times) took anywhere from 70-180 minutes depending on time of day. i ended up diving with
sea ventures. the dive masters were great and very professional. however, the diving was very lack luster. it had rained the previous night and vis was not great (30-50 feet obscured with particulate). there just wasn't much to see or do. we caught a glimpse of a ray and a turtle, but not much else. the coral wasn't very abundant or colorful.
the second day i went with
caribe aquatic adventures on a shore dive behind the normande hotel. this worked well as we stayed next door at the hilton. it worked out to a private dive, just me and the owner tony vega. this was great shallow water dive. we stayed within 100m of the shore, and never got deeper than 30'. as a result, we got ~60 minutes of dive (i'm still working on air discipline). i was amazed at all the sea life. it helped that tony knew exactly where to find it. if you're interested in getting up close to all kinds of small creatures on a personal dive this is a great way to spend a morning. perhaps the best part was that from leaving the hotel room to return the trip was around 2 hours. by comparison, driving to farjardo, diving, lunch, and return worked out to an eight hour day for less than impressive diving.
if you're willing to drive to fajardo, you have to
kayak the bio bay. that's got to be one of the coolest things i've ever done.