You can set up a Deputy for the time you are away - click the cogwheel ikon and choose Set deputy. If you are an administrator you can set up deputies for other users in AdminUsers.
The way it works is that invoices are sent to you as usual. If you log on first, you can approve your invoices. But if the deputy logs on before you, any invoices sent to you will be approved ofr you and sent on to the deputie. The Deputy setup will not include any invoices that are already in your inbox.