I'm one of the relax, read a book, take life a little slower, smell the flowers brigade. Knowing Portugal as well as I do, I would say this is asking for trouble. You haven't allowed for getting to the check in area, queues, traffic problems, train being late, etc. If you are refused embarcation, you will be annoyed with yourself, but if you are like most people, you'll vent your frustration on the check in agent. Is that really necessary?