The length of the update depends on:
- Other FSDT products you have installed, which will be updated too, if it's has been a while you haven't update them.
- If you have both FSX ( or a non-PBR version of P3D ) installed at the same time with P3D 4/5 so, even if you are installing GSX in 64 bit version, which only contains PBR objects, since you have installed FSX or a previous P3D version, it will download the latest "Legacy" ( non-PBR ) objects too, which must be updated for the other sims you have installed.