We establish the central limit theorem for quadratic forms Sigma(t, s=
1)(N) b(t-s)P-m,P- n(X-t, X-s) of the bivariate Appell polynomials P-m
,P- n(X-t, X-s) under time-domain conditions. These conditions relate
the weights b(t) and the covariances of the sequences (P-m,P- n(X-t, X
-s)) and (X-t). The time-domain approach, together with the spectral d
omain approach developed earlier, yields a general set of conditions f
or central limit theorems.