repeated measures

I have measures of community similarity at fixed sampling locations at two sites that were derived during five sampling dates. A repeated measures ANOVA using systat indicates a significant difference between sites and among sampling dates. But I am more interested in knowing when (i.e., during which sampling dates) community similarity differs between the sites. Can I use the univariate F tests for each sampling date that Systat gives when I ask it to provide hypothesis testing on the site effect?