I would tend towards handing my student over to another qualified instructor prior to sending them solo for a basic flight encompassing all of the appropriate maneuvers etc then once the solo is done and dusted the navs enter -i do operate on the FAA syllabus though and this is typical of many just to ensure that you have covered everything that is necessary- however i am unsure how it works in europe but a 4 hour solo cross country flight isnt unusual in the states (the candidate generally flys the route with and instructor prior to doing it solo)