For slopes lower than 4 the overlap is 18 inches half the width of the roll.
Roof dry in.
The roof sheathing is installed and a roof covering permanent or suitable reliable temporary roof waterproof.
What is dry in.
In short drying in a structure means that the roof has been protected with at least a layer of felt a product like tyvek housewrap has been installed along with all the windows and doors.
Because this roof is a lower slope than four in 12 they must overlap the courses significantly normal overlap of four inches.
Drying in for better lack of a term is making a house impervious to the rain or short for dry inside.
Roof dry in flashing and underlayment.