Zencast.Org provide a few meditation timers. I’ve modified their 60 minute one and created one for 80 minutes. I hope you enjoy it.

To keep our mind free from defilement under all circumstances is called ‘Idea-lessness’. Our mind should stand aloof from circumstances, and on no account should we allow them to influence the function of our mind. But it is a great mistake to suppress our mind from all thinking; for even if we succeed in getting rid of all thoughts, and die immediately thereafter, still we shall be reincarnated elsewhere. – Hui Neng