Initially 5 min, increased to 20 min. Phosphenes are not uncommon if the anode is too far forward and if the circuit is intermittent. Ramping the current up and down is a good idea. I would only use a battery powered supply myself. The video http://www.jove.com/video/2744/electrode-positioning-and-mon... mentioned above is excellent, incidentally (wooden acting aside).
Interesting video -- watching it made me realize that my ad-hoc "electrodes" were too small (2x2 cm), explaining the mild skin irritation. I wonder if it's common also to have a temporary, very moderate blurred vision in the right eye (only during stimulation)? It would make sense considering the cathode inhibits depolarization there. I'll keep reading.
Thanks for posting, this has been an interesting experience.
