The GFPT is a student pilot's privilege to carry pax in the training area and go for longer hours and calendar time between dual checks. It is an optional extra, and unless people want to carry pax locally, the GFPT is often a waste of time and money, and can also cause the student to lose momentum in their training. All the elements have to be retested at the PPL test anyway.. .Unless the instructor is behaving very irresponsibly then there should be no "risk" of bits of the syllabus being left out prior to starting nav training, as the student should be at the GFPT standard at the end of that phase of training whether they do the test or not.. .I would say that sending a student off on a solo nav which was more than three hours long is a bit much. It only has to be 150 miles long, so unless you are in an aircraft that cruises at around 50 knots or less (!) it shouldn't be a problem, even here in WA with limited numbers of suitable aerodromes for student solo.