San Juan and Boston share the same time during Eastern Standard Time (November to March). Both effectively use UTC-5/-4. When it's 12:00 PM in San Juan, it's also 12:00 PM in Boston.
Puerto Rico does not observe daylight saving time. During Boston's daylight saving time (March to November), San Juan is 1 hour behind Boston as Boston moves to UTC-4 while San Juan stays at UTC-4.
Best calling time: 9:00 AM - 5:00 PM works well year-round. During DST, San Juan is 1 hour behind Boston.
Boston has a significant Puerto Rican community. Many Puerto Ricans have relocated to Massachusetts over the decades. Direct flights connect San Juan and Boston in about 4 hours, with frequent service.