There is no time limit to the license. You can click on EULA at the bottom of the Magix site, go to Movie Edit Pro and read the license. Here is the link.
You have to remember that software becomes obsolete after a while. And Magix, like almost all other video and audio software companies, releases upgraded versions annually. As a registered user, you qualify for a discount. If you only use the software intermittently, you can skip a couple of upgrades. You can also never upgrade and keep using the version that you have purchased.
Once you have installed the software, make sure that you get the latest update or patch. As usual with software, there are usually 2 or 3 updates before the software maker goes on to the next version. By then, most of the bugs are fixed.
Lastly, Magix has built-in piracy protection. There is a monthly license check so you have to be connected to the internet occasionally. You can also install the software on more than one machine and activate the license for that machine or device, and then change back to the other machine a month later. This deactivates the second machine and re-activates the first machine.