July is behind the sommer timetable change in June Usually the Railcompanies update their timetable in March/April and publish it then for the summerseason :)  I recommend to plan with the actual times as there are usually no big changes in the times ;)

No, not strange at all, in fact very very common. as Sebastian explains-and he has done this by now at least 100+ times or so, trains are NOT planes. IF there are works somewhere along the line (and the longer the distance, the more chance on that) and with the modern insistence that all should be right to the very last minute, trains on certain dates will only be fed in the big system when the company (in this case Swedish Norwegians: vy.se) thinks it can now be definite. NO bus to bypass the works, maybe an hour longer-or not, etc. There really is no reason to worry and book 5 monthes advance.

Because: if that daily train on some dates has to depart maybe 30 mins earlier-early bookers may arrive too late and can then claim compensation. Thats the flipside of all this.

And anyone knows if there are daily trains from Stockholm to Kiruna? (on July)

There will be the same connections as currently the direct Nighttrain + the Nighttrain (in direction of Lulea) with a change in Boden to Kiruna :)