Is what we do — leaving early, signing in late, overlooking absences, and being lazy during the training period set by the college — unlawful, especially since we don't benefit practically and the employees at the institution behave similarly or worse?

What the workers are doing is not a favor but rather a dereliction of duty and laziness on their part, and you must adhere to the specified timings. If the trainers do not adhere, escalate the matter to the responsible authority to take appropriate action. It is not permissible to abandon the training program and collude with the trainers, and attention must be paid to the impermissibility of mixed-gender training.