Now would be the perfect time. In essence you'd be doing qt on your inverts while the tank is fish free. The 76 days will start once the last invert is added.
Also, since you'll be running copper, I'd highly recommend the Hanna test kit. It's pricey, but it's as close to 100% as it gets in this hobby.
Here's a link to the kit. You'll want to order extra reagents though since it only comes with 6.
https://hannainst.com/hi702-copper-hr.html
Here's the thread that brought it all to light. It also discovered the inconsistency with Coppersafe. I'd recommend Copper Power if you go chelated copper, or Cupramine if you choose ionic
https://www.reef2reef.com/threads/c...instruments-high-range-copper-checker.368943/