  YVO3 exhibits a well separated sequence of orbital and spin order transitions
at 200 K and 116 K, followed by a combined spin-orbital reorientation at 77 K.
It is shown that the spin order can be destroyed by a sufficiently strong
optical pulse within less than 4 ps. In contrast, the orbital reordering
transition from C-type to G-type orbital order is slower than 100 ps and goes
via an intermediate nonthermal phase. We propose that the dynamics of phase
transitions is subjected to symmetry relations between the associated phases.
