Well... depending on what you mean by how long:

You should try this for about a month[/b]
Reverse blinking should be done in a relaxed manner and consistently every 5 seconds. Sometimes I extend this time to 6 seconds and it works better. It's a really good technique if you can do it, I use it all the time to relax and etc. [/b]
I really don't know how long I reverse blink for, I haven't timed it - I just do it until I feel like I've said in my first post (falling into abyss, etc etc). Hmm, maybe about 10 to 15 minutes now that I think of it. Results may vary from person to person. [/b]