Refer jun 94 issue of Mechanical Engineering News.One example is illustrated about time history. the question is general, but the article is referenced for ease.Query is CAESARII applies all loads together , at same instance or in sequence? There is no way for the software to know that the loads will act one after other as the wave travels.TH1,TH2,TH3, TH4 all spectra act simultaneously ?

That's one of the major advantages of time history analysis - you can schedule your events in time. With time history you can follow the event through the system; with the (force) response spectrum approach, it's all on at the same time.

Thx Dave, but where do we input this info about wave travel direction ? Or is it that in jun 94 example ,TH1 acts first , then TH2 etc.But no start node or end node is specified

The events (applied forces) are defined and located in the Force Sets tab. The timing for each event is specified in the Time History Definitions. These two components are paired together in the Time History Load Case(s) tab.