Don’t make the mistake of waiting until you have a full-blown mosquito infestation before you seek treatment. If you do, the breeding population will be well established and it will be difficult to interrupt the lifecycle.
By getting treatment in early spring, you’ll have the advantage over mosquitoes. They may still hatch, but there will be far fewer than there would have been, and it will not be so easy for them to establish themselves. It may seem early, but you’ll thank yourself months later when you’re wondering where the swarms of mosquitoes went.