I think it very much depends on each royal. We know from documentaries and media profiles that Anne basically asks her charities and organisations she is linked to twice a year what if anything they would like her to do for them. These are then put to Anne twice a year for her to decide what to accept and not. Anne apparently is also of the attitude that whilst in London her diary is to be filled so if she has some time between engagements her office set about filling it. I presume by the sounds of it that Anne must basically give her team the dates she will work and the dates she won't and sets them to fill her working days as much as possible but with some key dates - state visits, investitures, commemorative dates etc factored in.
Ed and Sophie may well do the same but I guess as they live much closer to London they might not have quite the same attitude to "filling the time" as they can work from Bagshot a lot of the time and if there is a free evening etc they can go back home rather than spend the night in London whereas Anne seems to be a bit more "I'll spend Tues, Wed, Thurs and Fri morning based in London so fill that time". Ed and Sophie still have James in school and I imagine their children's commitments have also played a large part in diary planning - periods of exams etc.
Ed and Sophie may well do the same but I guess as they live much closer to London they might not have quite the same attitude to "filling the time" as they can work from Bagshot a lot of the time and if there is a free evening etc they can go back home rather than spend the night in London whereas Anne seems to be a bit more "I'll spend Tues, Wed, Thurs and Fri morning based in London so fill that time". Ed and Sophie still have James in school and I imagine their children's commitments have also played a large part in diary planning - periods of exams etc.