If you do a general google seach on salt water flush, you will come across protocols which suggest the 30 minute lie down. It gets the water out of your stomach faster.
Note: I have only done one SWF. Worked as advertised, but it also shot up my blood pressure from under 120/80 up to 170/110 within 90 minutes. Also note, that after 2+ years on the Liver Flush, I checked out my BP on that, too. Epsom Salts had no effect on my BP. It's been posted elsewhere that ES can lower your BP.