How do I schedule a task to run once?

While the java.util.Timer used to be a good way to schedule future tasks, it is now preferable¹ to instead use the classes in the java.util.concurrent package.

There is a ScheduledExecutorService that is designed specifically to run a command after a delay (or to execute them periodically, but that’s not relevant to this question).

It has a schedule(Runnable, long, TimeUnit) method that

Creates and executes a one-shot action that becomes enabled after the given delay.

Using a ScheduledExecutorService you could re-write your program like this:

import java.util.concurrent.*;

public class Scratch {
    private static final ScheduledExecutorService scheduler = Executors.newScheduledThreadPool(1);
    public static void main(String[] args) {
        System.out.println("Starting one-minute countdown now...");
        ScheduledFuture<?> countdown = scheduler.schedule(new Runnable() {
            @Override
            public void run() {
                // do the thing
                System.out.println("Out of time!");
            }}, 1, TimeUnit.MINUTES);

        while (!countdown.isDone()) {
            try {
                Thread.sleep(1000);
                System.out.println("do other stuff here");
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        scheduler.shutdown();
    }
}

One of the nice things you get by doing things this way is the ScheduledFuture<?> object you get back from calling schedule().

This allows you to get rid of the extra boolean variable, and just check directly whether the job has run.

You can also cancel the scheduled task if you don’t want to wait anymore by calling its cancel() method.

¹See Java Timer vs ExecutorService? for reasons to avoid using a Timer in favor of an ExecutorService.