I've found with "weekender" Cialis that it varies a good deal with me. Sometimes 10 mg is sufficient, sometimes it works only minimally. It could be psychological for all I know.
I make sure I take it at least an hour before I expect to need it, but I often leave at least two or three hours so I can be reasonably sure. I can tell when it's working by the swelling I feel in my mucous membranes. My nasal passages narrow a bit and my head feels like I have a mild sinus condition. The 20 mg size caused so much swelling that I couldn't sleep for an entire night due to the headache.
I've also found that the 20 mg size costs the same as the 10 mg, so I have the doctor prescribe the 20s and I cut them in half. I'm not sure if the remaining half stays good indefinitely as the original pill does.
