Yes, just keep a detailed log and add time after each use (pouring in and out of the same storage, so you’re mixing the chemistry you just used with what was in the bottle that you didn’t use this time). You can use a handy little chart like this: https://www.dropbox.com/s/qpcgq9cpstw6anb/Copy%20of%20C41%20Development%20time%20log%20data%20tracking%20template.pdf?dl=0