Is it permissible to browse legal websites for personal and professional benefit during working hours if there are no work tasks, and is extending departure time to include performing the Maghrib prayer in congregation considered a violation of Sharia?

The basic principle is to prohibit the use of work time for personal purposes, unless permitted by the employer or according to work regulations. Therefore, you must return after Maghrib prayer to complete the agreed-upon time. It is not permissible to resort to deception by having someone sign on your behalf, as this is forbidden deceit. You must repent to Allah for exploiting work time beyond what is permitted, and review what you have used from it unless the employer has allowed it. As a manager, you must look after the company and protect its interests, prevent manipulation by workers, and be a good role model for them.