When to pull taps on black walnut trees

I live in east central Minnesota and this is my first year tapping. I have a large black walnut grove (no maples) on my property and have taps in 10 trees. So far I have collected 20 gallons of sap, which should hopefully boil down to a couple quarts of syrup. I know the sap flow on black walnuts is quite a bit less than that of maples so want to collect sap as long as possible. The weather is starting to warm up to the point that I'm not sure if we will have many, if any, more nights below freezing by the end of the week. In addition to the weather warming I have read that spiles should be pulled when the trees start budding out. Since black walnuts bud later than maples does that mean I can leave them in longer? Any thoughts are greatly appreciated!

I have never tapped Walnut trees but I do know that you can surely tell when Maple sap gets buddy. It will have an off color and slight odor. I do not know why it would be different but maybe it is? There is no harm that I am aware of leaving them in and collect until the sap changes. If you are unsure keep the good sap separate from the questionable sap.

Thank you!