What is the ruling on praying Maghrib before its time due to work and transportation circumstances, and does ablution become invalidated by sleeping while sitting in a vehicle?

It is not permissible to perform the Maghrib prayer before its prescribed time. The distance mentioned does not allow you to avail yourself of the concessions of travel, such as combining prayers. Therefore, you are obliged to perform the prayer at its due time. You can ask the driver to stop for prayer. If that is not possible and you are in need of working, there is no sin upon you in combining Maghrib and Isha prayers by delaying Maghrib (jama' ta'khir) due to necessity. You should strive to resolve your problem. The ablution of a sleeping person is not invalidated if he is sitting firmly with his rear end grounded, according to the more preponderant opinion.