ミス廃用眼精疲労防止タイマー的ななにか
// timer widget
let Second=1000
var Count=0 // MUTABLE!!

while true {
  Core:sleep(Second)
  Count=Count+1
  
  Ui:render([
    Ui:C:text({text: `タブを開いている時間: {Math:trunc(Count/60)}分{Count%60}秒`})
    Ui:C:button({text: "リセット", onClick: @(){Count = 0}})
  ])
}
1

If you have a fediverse account, you can quote this note from your own instance. Search https://mi.tsujigoya.net/notes/ajb7rspx23 on your instance and quote it. (Note that quoting is not supported in Mastodon.)