In recent years, the scale of renewable energy is characterized by rapid growth, while issues such as the disorderly development of distributed PV and decentralized grid integration are gradually revealed, posing significant challenges to the safe operation and sustainable development of distribution networks. A planning model for rooftop distributed PV site selection and capacity determination that accounts for spatiotemporal differences is proposed, based on the spatiotemporal variability in rooftop distributed PV output and regional economic indicators of PV systems. First, considering the characteristics of spatiotemporal uncertainty of multiple sources and loads in new smart distribution networks, a PV-load spatiotemporal difference model is constructed. Next, the model is solved using a multi-objective sparrow search algorithm, taking into account the economic benefits on the user side, node voltage deviations, and system network losses. Finally, simulation verification is conducted using the IEEE 33-node distribution system as an example. It is demonstrated that the proposed model has practical significance for improving the economic value of rooftop distributed PV and the hosting capacity of distribution networks, while also providing valuable insights for the large-scale development of new smart distribution networks.