Given time to adjust to the device, the relief is immediate. They stay put when inserted; they do the job advertised. But the brain needs time to integrate the effect. Wear them with patience. Before you realize it, you will feel the ameliorative effect. And when that kicks in, you will recognize just how much they help. How noticable? Just take them out; the agitation of cacophony asserts itself, even more forcfully than before.
I live half a block from a busy and raucously noisy intersection, with loud, randy people gunning street racing bikes and rice wagons at all hours. These inserts have saved my sanity, and they've done the same for my daughter and granddaughter.
It's physics, and it works.