Hummingbirds will usually return to southeastern Connecticut around April 15, but you can put the feeder up as early as April first to feed early arrivals. Leave the feeder up until the end of September or as long as hummingbirds still come to it. Hummingbirds flying south rely on temperature, day length and other environmental cues to start migration. Your feeder may help them survive an early cold snap, but will not keep them from making their southward journey. Be sure to clean it regularly and replace with fresh nectar, hummingbirds can develop cankers from bacteria in the feeders, which can be fatal to them.
If your hummingbirds empty the feeder with greater frequency, clean it every time it's empty. Otherwise, once a week or slightly more frequently in hot weather. Cleaning with hot tap water works fine, or a weak vinegar solution, well rinsed. Cleaning brushes are helpful to prevent mold from growing in parts of the feeder.