What is the ruling on receiving money for a maintenance and follow-up contract for devices, knowing that the work may not require actual maintenance for months?

If a contract is made with the college for the maintenance of devices for a known period and a specified monthly wage, then the contract is valid, and the wage is due even if no actual work is performed, as long as you are ready to provide service when needed. It is not permissible to contract with the college at the same time as the one contracted with the university.