I had a barium enema test at 4 weeks post op to test whether the pouch has healed and to detect any leaks. You would have to have a similar test around that time, before your surgeon can decide to go ahead with the next step. They wait the result of this test to schedule the takedown.
I was in a condition similar to yours at my first step, I was in terrible shape and very weak when they operated on me. The surgery was laparoscopic, so the post op recovery was easy, but it took time for me to regain my strength, put on weight.
You are probably having a laparoscopic surgery on Monday, so you recovery will be faster. My second step was open surgery. I chose it over laparoscopic and it was a hard decision to make. The post op recovery with open surgery was hardcore, it was brutal. But, I finally had my takedown in March this year, and all that suffering is past memories now!
I had my first step at Mt Sinai IBD research center at NY, which is a major research organization on IBD. They wait two months between step 2 and 3 there. My second and third step were done by Dr Remzi at NYU, he was at Cleveland Clinic before. He is the world star on j-pouch redos, you can search his name on this website. He waits three months between 2 and 3. The surgeons at Mt Sinai NY and Cleveland Clinic operate on hundreds of pouches every year, these are the top j-pouch centers in the US. So, unless your doctor sees a particular risk in your case, waiting more than 5 weeks should not hurt you in any way. No need to worry about sticking etc if they ask you to wait 2-3 months.