I don't get this.

If I understand it correctly, the X-men films have two timelines. "The Wolverine" takes place in the first timeline. "First Class"
is in the second timeline.

X-Men: Days of Future Past starts off "In a dystopian 2023, robots called Sentinels have been programmed to hunt down and kill mutants" The actions taken in that film create a 2nd timeline and apparently the films after Days of Future Past (such as "First Class") all take place in the 2nd timeline.

They ignored Wolverine Origins because most everyone hated it. Though they screwed up other things continuity wise. For instance in the original X-Men movie Proffessor X says Magneto helped him build cerebro but in this movie it's built by Beast and other scientists. Not by Proffessor X and Magneto.

Also, making Mystique someone Charles Xavier grew up with feels wrong continuity wise since it's never implied they had known each other in the original trilogy. But they really wanted Mystique in these movies. Then again they make her a hero for mutants in the later sequels which also doesn't gel with things in the original movies.

Continuity in these movies never add up. There’s a ton of stuff that doesn’t make sense.