Non-coplanar magnetic orders in metallic helimagnets have been of great interest since the discovery of a vortex-like spin-swirling object called "skyrmion" and the resulting topological Hall effect in MnSi. A cubic perovskite metallic oxide SrFeO3 has been recently investigated as another example showing complex helimagnetic orders and metallic conduction. Quite recently, we have discovered that this system shows a long-time relaxation of magnetization in the helimagnetic ground state after cooling the sample under applied magnetic field. We suggest the possibility that the slow magnetic relaxation in SrFeO3 is attributed to time-dependent deformation in the skyrmion-like topological spin texture. In this proposal, we propose to perform time-resolved neutron diffraction measurements on SrFeO3 to directly observe the changes in magnetic structure.