For me there was no pain during my hospital stay as the intravenous pain meds were very effective, but I would say the first 2 weeks after the surgery were the most difficult, mostly due to discomfort and lack of sleep rather than physical pain (which was very manageable mostly through taking prescribed oral oxycodone). After about the 3 week mark I was completely off any pain medications and was using crutches full time and the experience became rather mundane. Again this is probably useless information to you as your experience will change dramatically based on where, who and what procedure you choose to go with. Good luck!
PS: Try not to get too caught up on the pain aspect of the procedure, as if this is something you are serious about the pain is only temporary. Children with leg discrepancies come every few years to lengthen their limbs until adulthood through more surgeries, so if they can do it you can!