Is it safe to say that for all non-rolling schools it does not matter when you interview? AND, more importantly, does this mean I can wait on these secondaries till I've finished the rolling ones?
Get them all in as early as possible. Although the decision is not rolling, interviews are offered on a rolling basis. If you submit your app early you will most likely interview early. If your stats aren't superb you may get passed over a few times and offered a later interview. If you submit your app late it may be harder to get an interview without excellent stats.