なんと小数点もいける(最小0.1まで)
watch -n 0.3 -d "xxxxxxxxx"
これはDebian bookwormのDockerイメージでman watchを実行したものだけれど、MacOSのman watchも全く同じ文言だったので、0.1が最小なのはFreeBSD系でもGNU系でも変わらないっぽい。
-n, --interval seconds
Specify update interval. The command will not allow quicker than 0.1 second interval, in which the smaller values are converted. Both '.' and ',' work for any locales. The
WATCH_INTERVAL environment can be used to persistently set a non-default interval (following the same rules and formatting).
