@delay

@delay <ms> { … } applies a block once, after a pause — a "Copied!" flash, a toast that hides itself, an undo window — with no timer in JS.

Writing a delay

button[data-copy] {
  @on click {
    data-copied: "";
    @delay 2000 { data-copied: none; }   /* rapid clicks restart it */
  }
}
output[is-visible] { @delay 4000 { is-visible: none; } }
todo-item[is-pending-delete] {
  @on click (target: "[data-undo]") { is-pending-delete: none; }
  @delay 5000 { is-deleted: ""; }         /* dropped if undo clears the gate first */
}
[data-flash] { @delay +attr("data-flash-ms") or 1500 { data-flash: none; } }

The duration is any expression — a literal, a binding, an attr() read, arithmetic, a quark:math call — in milliseconds. The block is an ordinary rule body: declarations write the matched element, nested rules write its matching descendants, and it may hold another @delay or a @view-transition. @on inside the block is not supported.

When it fires

• The timer starts when the rule applies to the element, or when the event fires inside an @on block, and restarts on every application — one timer per element. A rule re-applies when its selector's dependencies change, so a rule that fans out on unrelated attribute changes restarts its delays too.
• When the timer fires, the block applies only if the element is still in the document and the rule still matches; otherwise it is dropped. That is what makes the undo idiom above safe: clearing the gate cancels the pending write.
• Inside an @on block, event and target keep the values the block was scheduled with.
• Pending timers are cleared when the sheet unregisters.

Safety

The block keeps the loop guard's causal depth of the run that scheduled it, so two delays that keep re-triggering each other are cut like any other runaway chain instead of ticking forever.

Time is otherwise an Adapter's protocol: @delay is for a wait that belongs to one State change, not for clocks, polling or animation — those are elements (<timer-…>) and CSS.

DevTools sees every timer as a ["quark", "delay"] publication: scheduled (with ms), fired, or dropped (with reason: "disconnected", "unregistered", "unmatched") — see JS API.