Slight correction. 終わり rather than 終わる. (Easy typo to make.)
This is correct. And it has an extra grammar point when following the volitional form.
Here’s a good link for it: How to use volitional form in Japanese: V(よ)う (maggiesensei.com)
- Volitional form + とする ( = to suru) /としている( = to shiteiru)
(1) about to do / about to happen
Something hasn’t happened yet but it is about to happen /It will start to happen soon.
You don’t usually use volitional form for things you can’t control.
However, even if it is something you can’t control, you sometimes use volitional form if you are somehow involved in the event.
You often use this pattern to describe some change that involves you — especially in written form or a formal announcement.
Although Yuuki has no control over when fourth period ends, fourth period ending certainly does involve him. I’m guessing this qualifies as “written form” here because it’s not Yuuki speaking or thinking, it’s narration (being in a rectangle box rather than a speech or thought balloon).
Including that として (from とする) gives the sense of “to try to …/to be about to…”, this may translate as: Right now, fourth period is about to end.
@rugoseappendage: If you feel you would benefit from a detailed explanation of としている or any other part of the sentence, don’t hesitate to ask. I know it can be difficult to take in new grammar by reading through resource material that covers a wide variety of situations. I or someone else can reiterate and simply if needed. I’d have gone into more detail here, but my time is limited this morning.