Re: when is it time to pinch a queen
Some queens cut way back on brood if the flow stops. Others not so much. In my experience, the darker bees such as carniolans will slow way down on brooding when the flow slows or stops, much more so than Italians. If that is not the case with you, then I'd say yes, pinch the queen and add a cell. You may do that reguardless, if the nucs in question show a lack of performance compared to others in your yard. That is one advantage of having several or more nucs/hives, as we can see comparison differences between hives, which helps us in our management decissions.
20+ years, raise my own queens, feed when needed, I treat but have not perfected varroa management yet.