Is it permissible to take payment for two hours of overtime work without the employer's knowledge, or must one leave them as a debt upon her until the Day of Judgment?

If the pharmacy owner obliges the worker to work two additional hours beyond what was agreed upon, and then refuses to pay for them, the worker is permitted to take the equivalent amount without her knowledge, based on the opinion of some scholars regarding the issue of al-Zafar (taking one's right without the oppressor's knowledge). However, if she worked the two hours voluntarily, without being compelled, she is not entitled to any payment for them.