If you are dead set on still measuring. Put the sample into a container that you can whisk, take a whisk to it every hour for several hours, and then let it sit out at room temp overnight. Whisk it one more time in the morning to release any residual C02, and then measure. If you try to shortcut these instructions, IME, you're very likely to get a bad reading. Just an FYI. Been there. If it tastes done, I probably wouldn't worry about it. I can usually taste about where one of my regular recipes is based on it's dry/malty body, but I've had lots of practice at it, and while that's good enough for me, it's not giving you an exact reading.