My general approach is to slot level 25 generic IOs upon hitting level 22, then continue to craft and slot them until I hit 50, at which point, I'll start to accrue reward merits or Inf to either fully slot out one of my other builds or just replace those 25 IOs as I go. If you keep them on that initial build, you'll retain their full effectiveness should you choose to do lower level content, (at least to greater degree than if you were trying to use 50+ IOs on a Yin TF or something).