They mean in the past~
Okay, okay, I finished chapter 15. I TOTALLY THINK IT’S KAZUO WHEN HE SNEAKS OFF “TO THE STAFF ROOM”. Also, she was damn lucky her classmates didn’t kick up more of a fuss. And why didn’t the teacher follow up about that?!
I digress. Tsubasa Bunko ed.
Page 86
教室の中のだあれも君が教室から出て行くのを見たものはいないんだ。
Quick check: is that だあれ just an extended だれ?
Page 87
Apparently @xarde had trouble with the exact same part of this sentence as me, but they figured it out and I still don’t get it even after their breakdown 
かれらにすべてをうちあけたのは、ずっとあとなのだし、うちあける原因になった事件そのものがまだ起こっていないのである。
Okay, is the last part (in horrible literal translation style) “the incident that became the source of what she confided hadn’t occurred yet”? Struggling a bit with the 原因 bit.
And then I totally don’t understand what the middle bit in bold means.
Page 89
和子がぐっと胸をそらし、手足に力を入れたとき。。。
First off, here we meet 手足に力を入れる again - so glad I managed to remember that a mere 24 hours later 
on which note, jeez, they cracked out a lot of さえs this chapter.
Anyway - just not sure what そらし means.
I also read this chapter super fast! 
That’s what I assume 
More like the incident that became the reason (原因 comes here) to うちあける hadn’t occurred yet. 原因 as cause/reason.
As for the bold part, あと is 後 like @xarde pointed out, and ずっと後 means that this particular thing (かれらにすべてをうちあけたのは) happens a lot later (ずっと is a very versatile word, so that might be confusing). The next bit with 原因 kind of elaborates on this saying that the whole reason to tell them the stuff hasn’t even happened yet.
You’re probably going to be mad at yourself, but it’s that old thing where they end things on the ます stem. This is just 胸をそらす 
Yeah, I think I was just struggling with the relative clause for some reason, and then it didn’t help that I was thinking ‘source’ rather than something useful like ‘reason’! (“origin to confide???” I said to myself…)
Ooooh. I just did not get that bit. ずっと does indeed often trip me up.
Now, see I am mad at myself, but I wasn’t tripped up by the stem. Where I screwed up was searching for そらす rather than むねをそらす, as jisho is incapable of matching things which don’t start at the beginning of the string. Gah!
Thanks so much as always 
Sure it is, it just doesn’t do it by default! Put an asterisk (*) in front to find things with more in front, or an asterisk on both sides to include things where it’s in the middle. The default search is the same as having an asterisk after.
You can even throw in asterisks in the middle if you want!
WHAT 
why didn’t I complain about this sooner
Welp, at least now you guys know why I kept asking for definitions of things easily found in the dictionary
Not necessarily a translation question from chapter 15, but just clarification.
二重存在の矛盾は、未来の和子ーーつまり帰ってきた和子がこの時間に現われると同時に、もうひとりの和子の姿を消すことによって、解決されるのだ。
教室にいた和子が、ふいに消えたその時間は、未来からタイムリップによってもどってきた和子が、自分のへやに現われたのと同じ時間なのである。
She seems to be explaining to herself that when she came back here from the future, the Kazuko who was in class disappeared at the same time that she appeared in her room (and that the situation was “resolved” in this way).
Side note, I like the phrase 二重存在の矛盾. I know she was previously worried about there being two of her, and we’ve seen multiple times now that that hasn’t been the case. But I still wonder about the mechanics behind the teleportation/time leaping, and what (if anything) is felt by the Kazuko whose place is taken (so the one who disappeared from class, for example).
Really really rough translation…
“The contradiction of a double existence (ie there being two of her), the future kazuo, in other words, at the same time as this kazuo returned to this time, the other kazuo’s form dispeared, which solved that paradox. At the time when the kazuo in the classroom suddenly disappeared, that was the same time that the kazuo who returned by time leap from the future appeared in her own room.”
Oh also, in terms of the second kazuo, yeah, that is weird. Time travel always leads to strange consequences. Is the past kazuo erased? Are there parallel universes? Does the past kazuo experience time travel? etc.
She probably got eaten by the langoliers. No time for pain.
Langoliers 
For real though, if she gets eaten by this then DDDD:
Something I’ve been doing a lot on jisho lately is add each new word at the beginning of the search with a comma afterward, then I can look up a bunch of words in one tab.
I usually come back to it and add them to Anki at some point.
It’s especially useful on my phone. I used to open a new tab for each word, and there’s a max of 100 tabs on the phone Chrome browser lol
Nice hint. 役に立つ
Thank you~ I see the definition in Jisho now
Happy I was (kinda) helpful @Radish8
My reaction also!
Oh my, this opens up whole new adventures! 
I’m glad it wasn’t a revelation to just me!
@Darcinon thank you so much for the tips. Can’t believe how much more efficiently I could have been doing this.
Nice, is that a browser extension like Rikai-chan/Rikai-kun? I used to use that back in the day. I’m reading this book using the ebookjapan mobile app though, so those wouldn’t work. (Of course I could read on a computer with the web reader instead if I really wanted to. I’ll probably do that for 少女終末旅行 if it’s too small.)
@Radish8 fantastic, I’m glad to help! I’m a computer-oriented problem-solving sort of person, lol (my job is mostly web development)
By the way, the reason the commas work is because you can actually copy in sentences and Jisho will attempt to parse it and add furigana and links to definitions. Sometimes it doesn’t do a very good job though. The commas help it out, at first I was using spaces and it was having issues parsing words pretty often.
Yes, it is an extension similar to Raika-chan. I have never really seen a manga e-book so I am not sure, but I suspect that in case of manga everything will be a picture, including text, and if that’s the case the hover lookup might not work…
Well after being behind schedule for such a long time. I kept reading (coz the story was fun) and reached chapter 17. Things are about to get interesting!
Sorry, I can’t help myself.