  We present an investigation of the magnetic field-temperature phase diagram
of Cu$_2$OSeO$_3$ based on DC magnetisation and AC susceptibility measurements
covering a broad frequency range of four orders of magnitude, from very low
frequencies reaching 0.1 Hz up to 1 kHz. The experiments were performed in the
vicinity of $T_C=58.2$ K and around the skyrmion lattice A-phase. At the
borders between the different phases the characteristic relaxation times reach
several milliseconds and the relaxation is non-exponential. Consequently the
borders between the different phases depend on the specific criteria and
frequency used and an unambiguous determination is not possible.
