Do I cast them on then not K or P until the next time around?
You have to work them on the same row you added them in order to get to the existing sts of that same row.
As depicted here, and in my prev post, the 5 new sts are now at the working end of your ndl. In order to get to the old Ps (red)...the ones that were there before you CO... you have to work P5, P4, etc to reach them. (Your working yarn (to your skein) is attached to P5.) You work them in the reverse order you put them on your ndl.