For example, this is what rclone does one the same folder by only checking files by modtime&size:

```
Transferred:             0 / 0 Bytes, -, 0 Bytes/s, ETA -
Checks:               179 / 179, 100%
Elapsed time:         0.0s

real    0m6.932s
user    0m0.129s
sys     0m0.022s
```