*MISSABLE* Each level has a maximum number of points to earn, which is shown at the start of the level in the top right corner of the screen. As time passes while you are working to finish the level, the score depletes. Once you complete the level, you are awarded the current score that is shown. If you take too long, you can earn no points on a level. The score you earn from each level is added to your total from all of the levels. Speed is the key here. The faster you complete the level, the more score you will earn.
These achievements require that you earn a cumulative score of 250,000 and 500,000 in a single playthrough (one save slot). These are both technically missable, but by using solution guides it will be hard to miss these. In completing all 50 levels, you will most likely earn 1 million score or more and will probably surpass the 500,000 point mark around Level 30. To make absolutely sure (though it is unnecessary) that you earn these achievements, you can replay a level that you think you can go quicker on by not hitting "Save and Continue" after the level, and returning to the Main Menu with the Back button.