Regular nios student can give exam one time in a year . In on demand you can give exam every month . Date can take as per your choice . You can take gap between 2 subject exam. If you fail then you can apply again in next month but not in the month of regular exams.

As of ODE, you won't be able to give exams for more than four subjects. Five subjects will be like giving full examination and it won't be considered ODE.

If you had appeared for other examination, and have passed atleast one, you may not need to appear for all subject. Suppose among five subjects, you had passed 3 and failed 2. Appear ODE for only 2.

Hope it answers your queries.