If the *.tmp files are around after the machine has been restarted, they are typically no longer needed. Tmp files are generally generated during a file operation where data in memory, or larger than memory allocation is *temporarily* written to the drive.
So ...... you should be able to delete all those old tmp files.
If file allocation data is changing that much, you may want to start a defrag of your drive before leaving for the evening, and/or validate your drive.
All good things for drive performance and health.
