Most summer timetables should already be available. Which countries/routes are you looking for?

Italian long distance trains for the summer timetable (from 12 June) should be available in the latest app update. If you don't see them, please check for an app update. Italian regional trains are not available yet because Trenitalia has not published them yet. For most other countries, summer timetables should be available.

However, you should not use the app to plan, since it does not get enough updates to be reliable (only about once per month). National websites and apps are more complete and up to date. For international planning, the German railways planner or DB Navigator app is good (updated twice per week).

It MAY always be the case that last-minute changes have to be made-and railways/treni are always prone to ´ritardi´ in some countries much more as others. Or-you should know it- strikes (scioperta). In most cases if there are f.e. works along the lines, then the planners will be adapted to that. But for rough planning simply use -best for same day of the week- for may/june of there are no tinings yet for agosto

As a very rough rule one may state that the further north you go form la bella Italia, the beter it gets. The main pronlemi for most on this forum is getting the REServazione that you need for many trains in some countries.