Keep in mind that you can take the test whenever you want but you will not get the certification until you have 2 years experience in the field. The tests are multiple choice. If you are good at taking tests, you can study for them and probably pass most of them. I am a former ASE Master Tech, also formerly certified in Advanced Engine Repair (L1). I took 4 tests one night, then 4 tests a week later, and passed them all, but I studied my *ss off and I do very well on multiple choice tests. Some topics like engine repair, brakes, suspension, I had covered but others I had to study for, like auto trans, since I never touched a transmission. I passed that one by one point.
You didn't ask for it, but here are my two cents on automotive education. Any course that gets you a college degree, like a B.S. or an Associate's degree at a minimum is great. Don't spend $30K and walk away with just some certificate. If it were me I wouldn't spend significant money unless I walked away with a degree from an accredited school. Better yet, go work in the business and see if you like it. Lots of guys never went to school but instead gained experience on the job. I did it this way although I only worked about 2 years in the field. Dealers won't hire you, but private shops will if you start at the bottom. Get a feel for the industry and work your way up as you gain experience. Sweeping, oil changes, tires, brakes, parts changing, engines, diagnostics, electrical, computer controls, in that order more or less. If you hate the industry then get out and don't look back. If there is something there that is calling you, then either go to school or work your way up through a private shop. Whatever you do, don't spend $30K on school without getting a taste of the industry first. This is just one guys opinion. I sure some will disagree and some have taken different paths that have worked just as well.