@neauoire First check your libs, perhaps the file is installed in some non-standard location?
sudo ldconfig -p
And there search for libporttime.so output.

Should be something like this:
libporttime.so.0 (libc6,x86-64) => /usr/lib/libporttime.so.0

If is not there, you can install portmidi package and link your libportmidi.so to libporttime.so like this:
ln -s libportmidi.so libporttime.so

Then reboot your system and should be fine now.