I did this it took 1 hour for it to do anything. It took 1 and ½ for it to fully take affect. I thought that was a long time, I had originally given up concluding that it didn't even work.
Unforutnatly through a mix up, I found out I had a doctors appt. that day, that I really couldn't reschedule.
The nurse said to me... "wow your heart rate is really up there." She was waiting for an answer but I silently sat there. It lasted a really long time. I'll do that again on a day when I'm sure I have no obligations.