So. You will work until you are tired. Then stop. Because you say you will work without being tired. But when you ARE tired, you'll stop. Bit like "giving 110%"...a. brings into question the concept of infinity, and b. indicates you really can't be trusted as you tell big porkies from the outset.
"We will work tirelessly" is the kind of phrase you usually only get in customer-service type letters where the writer is in an indefensible position after some ghastly cockup and is trying to make as many weaselly excuses as possible to try and make out his organisation is taking the matter seriously. I wouldn't trust the writer.