If you run your bttn on batteries, it goes to sleep after each press to save power*. When you press it again, it wakes up, and this takes some time.

- This is fine for most non-real-time applications, but if necessary, there's a simple thing you can do to eliminate the delay: Run the bttn with a USB power source. Then it will not go to sleep, and your action will be performed in 2-3 seconds.

* Thanks to this battery saving feature, your bttn can perform even up to 800-1000 pushes with one set of quality alkaline batteries.