No there is not yet.

But simply look at a decent planner, f.e. from bahn.com or its own site-click on train nr-what the from/to dates these yr is-will likely be the same +/- 1 day. On some shorter sectors with more demand there seems to be the odd train in a longer period.

Generally speaking in SE holidays tart from midsommerafton=the longest day, but in the north it can have frost till in may, or not the best time to do these things

Anna fra sverige will likely know.

Here you can look at the timetable for this year. Yesterday was the last day of this year's summer season.

https://res.inlandsbanan.se/en/timetables

Even is reservations not are mandatory on Inlandsbanan I strongly recommend you to make reservations as persons without reservations only can travel if there are free seats. As Inlandsbanan often is fully booked you take a big risk if you try to travel without a reservation. 

The train is not shown on bahn.de and so on.
Just check on the link from Inlandsbanan. Next year will be similar period (start around mid/end of June, end about end of August) and also similar timetable.