How to use hardware acceleration with FFMPEG for trimming and concatenation purposes
Since you are using -c copy in your commands, there is no decoding, filtering or encoding taking place and so hardware acceleration isn't relevant at all. The main bottleneck is disk I/O. On a regular internal HDD (with a 3rd gen CPU) I get speeds of 400x so I suspect you're reading or writing to an external drive. Or your internal drive could be slow, have a smaller cache. The biggest boost will come from writing to a different drive than the drive on which the inputs reside, with ideally both drives being internal.