We used to do PeriOp 101, but because we haven't had enough open positions in recent years, we haven't had one for quite some time. When we did, it was a 6 month orientation with a preceptor, and didactic was spread throughout the first 2-3 months. This was then followed by three months "flying solo" while a preceptor backed up 2-3 newbies while doing their best to stay out of the rooms. New nurses were able to start before the internship, but only by a few weeks. I personally started about 1 month before the official beginning of my PeriOp 101 class, and primarily followed another nurse around without doing too much until class began. The classroom part took place in the educators' office, which was large enough for our group of three to fit around the table. Not sure about when they had the larger classes up to six. Haven't seen a class larger than six.
Now, it's a six-week orientation that combines classroom and clinical, but classroom takes place with cath lab, ep lab, other areas, and some (possibly most) doesn't apply. Of the three nurses hired on this program, two have quit and only one has stayed.