It's quite straightforward - a CPL requires 200 hours. If you get an IR afterwards you'll need to do at least 45 hours of EXTRA training. But if you do the IR first, you can include the IR in those 200 hours. It's like having the aircraft for the IR training for free and only paying for the instruction. It's the biggest open secret in flight training. The bonus is that if you do an SEIR, you "save" the ATPLs. You don't need to bother keeping it current - when the industry recovers you'll need to convert to MEIR anyway.