All Dutch universities use the so-called bachelor-before-master rule. This means that you first have to completely finish a bachelor’s program or transition program before starting with a master’s degree program.
All TU/e master’s degree programs have at least two starting moments for external students; at the beginning of the first and second semester. You could start with your master’s degree in September or February.
Are you finishing a bachelor’s program or transition program at TU/e? Then you can register every month, as soon as you have graduated from your bachelor’s program.