Why would anyone want to do 24 miles of Shikko? That's just asking for knackered knees.
Shikko is, in my opinion, harder to grasp then a good Ukemi. It took me ages to realise that you have to bring your knees together, move the hips, then move the kness apart and start again.
Practice for 5 minutes before each class and get a senior student to have a look at your techniques, but DON'T spend hours trying to master it if you're technique is incorrect.