What is the ruling on shortening agreed-upon working hours and making them up later without informing the employer, and is it obligatory to return the money earned from that shortening, or is repentance and compensation or giving charity sufficient?

It is not permissible to lie about working hours or to claim wages for hours not worked, because a private employee's benefit is measured by time, and their services are owned by the employer during the period of hire. As for the past working hours for which wages were taken, the original principle is to inform the employer or return the wages to them by any possible means, without needing to inform them of the reason. If this is not possible, it is hoped that compensating for those hours will suffice for the questioner if she delivered the contracted services to the employer at the required time.