Improving the single-instance IPC

Problem

Some file explorers open multiple folders with `process folder1 & process folder2` instead of `process folder1 folder2`

If "folder2" takes

between ,5 and 5 s to recurse it remove the playlist entries added by "folder1"

longer than 5 s to recurse it's opened in a new instance

Solution

Improving the ,5 s limit by counting it from when the previous instance finished rather than started opening

Removing the 5 s limit