The most consistent time to use body fat scales is in the morning, right after waking up. This minimizes variable factors like hydration that can occur throughout the day, affecting measurement accuracy. Emptying your bladder before using your scale also helps with consistency.The most consistent time to use body fat scales is in the morning, right after waking up. This minimizes variable factors like hydration that can occur throughout the day, affecting measurement accuracy. Emptying your bladder before using your scale also helps with consistency.