Only accept timestamps without leading whitespace and which are large enough
to possibly be a timestamp

One simply should not close System.out ...

The expired flag of an expired timer was not properly cleared before queueing it again.

A newly created timer was always considered as running.

This avoids the overhead of maintaining the selectedKeys() set

After the timer rewrite only the timer callbacks are executed
but stages are no longer automatically marked for execution. Timers that
send messages are not affected as that uses the standard activation mechanism.