It would be helpful if you would tell us what area of study you are asking about in this question. Real time assessment could refer to a number of different areas, from education to medicine.
In general, real time assessments are ones for which it is not necessary to wait a long time to get results. For example, real time assessment can be used in educational settings. This has become more easily done with the increasing quality of computers. A real time assessment might involve a student inputting his or her answers and then being told right away whether the answer given was correct. The best of these systems also have explanations. These systems can tell the student what the right answer would have been and can point out commonly made mistakes.
This term generally refers to assessments that can give feedback instantly. However, the specifics vary depending on the field of study that you are talking about.