Why not just use the device and see if the battery holds up for your daily use? If it doesn’t, then replace it. If it does then don’t replace the battery until you need to.
I'd replace it. I actually got an 8 Plus in January w/ 87%, and one of the first things I did was get a $49 Apple battery replacement. So glad I did, it's like having a brand new phone!
I'm at 83% on my 7+. While I do have to charge it 2-3 times a day, it's still not that bad. I'd wait a few months then get it replaced so you get the most for your money/time.
As it turns out my 8 Plus has 86% health. I'm not having any issues with it to make me want to change the battery. It feels strong, like it has another year before it would need a replacement.