AFAIK, it's nothing to do with the SSD, but the native setting is to wait 20 seconds for every single software that not responding during shutdown. So, if you have 20 stuck process. That will cost you 5 minutes waiting time. If you have 100 non responding process, that will cost you 25min to shutdown. Amazing Apple default that long to wait but not just kill the process. TBH, I don't think they really that care about losing data.
There was a simple script available back in Mavericks specifically deal with this issue. It change the 20s waiting time to 1s, therefore, greatly speed up the shutdown time. It works all the way to Sierra, but not sure if that still work in High Sierra.
It may cost you some time to search that script (it should be somewhere in the OSX forum, most likely in the Mavericks forum), but worth to try.