Adding new form fields based on the value of another field

You should create a new table called perhaps Labor Days and then set up a Relationships where One Project has Many Labour days. The fields will be the date (which you can set to default to today if you like), and the Num. Laborers and the Num. Hours. 

Embed the child table on the form so you can see the Labor Days entries and Quickbase will also make you an Add Labor Day button for the form. 

You can easily create a summary field on the relationship to roll up the total hours up to the project Project  

Here is some help on Relationships.