8:12 PM
I kind of have something of an idea, if you must know, @Sanath, but it's not entirely interesting.
@Sanath digression : if you have an algebraic variety X over $\bar {\mathbf Q}$, and you have the corresponding dessin $\Gamma_X$, shouldn't $\text{Gal}(\mathbf Q(X)/\mathbf Q)$ act on $\Gamma_X$ by isometries?
was just wondering, because if it does, then this galois group must also act on the collection of little nbhds around the nodes of $\Gamma_X$ on the corresponding $\{0, 1, \infty\}$-branched Riemann surface transitively, so one should be able to realize this thing as a subgroup of automorphisms of the Riemann surface.
and then one should be able to tell something about the order of this, I suppose, by Hurwitz's theorem.