Mean sky background at the OAJ in bands J0430 (green), J0660 (yellow), and J0861 (red) as a function of the distance to the Moon and the phase of the Moon: 100% (Full Moon; thickest line), 90% (medium thickness), and 0% (New Moon; thinnest line). This information, computed empirically in advance for all J-PLUS bands, is employed to derive the exposure times in real time that are required to reach the planned J-PLUS limiting magnitudes.