If you're looking for a meeting place or a good stop around ½ or halfway between Guilford and Block Island, you can try Westerly, RI, which is about 1½ hours east of Guilford, or about 1½ hours northwest of Block Island.
About ¼ or a fourth of the way, you can stop at Jericho, CT. This is about half an hour east of Guilford.
About ⅓ or a third of the way, you can stop at New London, CT. This is almost an hour east of Guilford.
About ⅔ or two thirds of the way, you can stop at Charlestown, RI. This is almost 2 hours east of Guilford, or about 1 hour north of Block Island.
About ¾ or three fourths of the way, you can stop at Narragansett, RI. This is about 2 hours east of Guilford, or about half an hour north of Block Island.
If you drive straight through without stopping at all, the total distance is 95 miles. The distances shown above don't include local roads to get into each town, so if you're planning a long road trip, make sure you factor in traffic and road conditions, rest stop breaks, and interesting detours along the way. If you're in a rush, you can do the trip with zero stops, and your total travel time would be around 2 hours, 47 minutes.