Apon Launching and playing the game you will get one achievement every second(or close to this). If you close the game without getting all achievements, the next time you launch the game you will have to wait until you reach the timer count you reached last time you played to continue the achievement flow.

EDIT: sometimes launching the game will continue flow of achievements.

To get 100%:

There is 1505 achievements and you get one every second. 1505/60 is 25
which means to get 100% achievements you will have to keep the game launched for 25 minutes without closing the game.

Writing this took me like 10 minutes (so much effort u know) so it would be greatly appreciated if you RATED and FAVORITED thanks <3.