Tracking API - out of order events

Does anyone know what effect it will have if I’m calling the tracking API and over-riding the time of the page view, and these calls are out of order? The reason I’m asking is that I’m processing quite a lot of historical data and it would be a lot faster if I can fire the requests on multiple threads, however this could result in out of order events and I don’t want those messing up any statistics on page view time / session length etc.