Do not leave them on 24Hrs. This WILL enable more lidocaine into your system and become problematic.

I have seen posts in the past where doctors have even told pain patients to leave them on 24hrs. That should NEVER be done.

I have never used more than one. In fact you can get substantial relief from 1/2 or less depending on where you put it.
Placement is everything for these. If you put them in the WRONG place, they don't work, and may cause more pain...throbbing etc. Putting on end points of perceived pain doesn't work well. Placing them over the path the nerve takes to the spine, is best. They don't work instantly and need every day attention. They totally stopped my severe MP pain within 14 days of use--in a row. I had that nasty pain for years, and it is mostly gone now. A little twinge if I overextend the leg too much but that is nothing compared to what I had before! I think the lidocaine stopped an overfiring nerve, and the nerve stopped doing its thing and forgot to overwork. My thigh is no longer numb either! I consider that the best pain intervention I have ever had!

Even when using on the back you can get by with 1/2 on each side. I have done that in the past.