Does preoccupation with work, exams, or driving a car count as heedlessness of God, even with performing the prayer on time?

Negligence has degrees. The highest degree is preoccupation with worldly matters and their desires, coupled with neglect of religious duties and abandonment of work for the Afterlife. As for the negligence that does not cause harm when one is engaged in worldly matters, provided that duties are fulfilled and prohibitions are avoided, it is a relative negligence from which hardly anyone escapes. It is better to continuously remember Allah and contemplate matters of the Afterlife, but "an hour for this and an hour for that" is permissible. Negligence has sometimes been considered a necessary blessing for the well-being of this world and religion; it is like salt in food, praised when it is in moderation and condemned when it increases and leads to neglect and self-abandonment.