If you just purchased these perennials in containers from your local retail store, they probably won't need to be divided now.  The time to divide depends on the type of perennial. So I would go ahead and plant them, frost and weather permitting.  Please see the two below references for further details.

Dividing Perennials | Home & Garden Information Center

https://hgic.clemson.edu › Factsheets Sep 6, 2019 — Spring division is ideally done in the early spring as soon as the growing tips of the plant have emerged. Spring divided perennials often bloom a ...

How and when to divide perennials | UMN Extension

https://extension.umn.edu › dividing-perennialsHow to divide perennials. Dig up the parent plant using a spade or fork. Gently lift the plant out of the ground and remove any loose dirt around the roots. Separate the plant into smaller divisions by any of these methods: Each division should have three to five vigorous shoots and a healthy supply of roots.