Not needed. If you want use in first couple weeks of flower then cut it. I stopped using rhizo when they changed the formula, doesn't work nearly as good now.
+1, mine went bad over the summer, so I dumped it.
Still had some Rootcomplex left from Hesi, works as well and I have had the stuff lying around for ages, it has no issues.
To OP:
I wouldn't really use it in flower unless you wanna transplant and then flip pretty quickly, or have really short veg times in general maybe.
But surely there's no need for it after week 1 or 2, as being said.