There are direct flights Lisbon-Bissau with TAP (http://www.flytap.com/) three times a week, all arrive currently at 01:10 am, returning the same day. Senegal Airlines also flies from Dakar (http://www.senegalairline...).
TACV (http://www.flytacv.com/) have four flights each week from Dakar to Bissau, returning to Dakar the same day. These flights are not an example of punctuality and it is a good idea to check with the TACV office in Bissau Av. Amilcar Cabral 8B, tel. 206087 before you head to the airport.