The compounds Bi1-xSmxFeO3 exhibit concentration- driven transition from the polar rhombohedral phase to the anti-polar orthorhombic one and temperature- driven transition into the non-polar orthorhombic phase. The compounds having the compositions corresponding to the phase boundary region between the polar rhombohedral and anti-polar orthorhombic phases (0.1 < x < 0.14) are characterized by most pronounced magnetic and electromechanical properties due to metastable structural and magnetic states. These compounds exposed to the temperature- driven structural transition are characterized by a time-lag of about two-three days attributed to the structural relaxation process as compared to the immediate modification occurred in the magnetic state. This unusual feature allows to clarify a correlation between the crystal structure and magnetic state using temperature neutron diffraction measurements.