"क्या तुम इस समय अपने कमरे में हो?"

Translation: Are you in your room at this time?

[jetsconnor]

I don't understand when to use इस instead of यह...

[RanzoG]

The sentences is tricky because the Hindi version has a postposition that is only implied. Look at the English; the phrase is "at this time." While the Hindi sentence has left out a word corresponding to "at," we still understand it to be there. And it being there puts the phrase "this-time" into the oblique case. (इस is the oblique case transformation of यह.)

[ihavelonghair]

I’m curious why they combined tum and apne. Why not use tum and tumhare, or aap and apne?

[RanzoG]

apnā = "one's own", and it must be used (instead of all the other forms) when the subject of the sentence is doing the possessing. "tum" is the subject of this sentence, so you can't say tumhaara, you must say apna.
There's a logic to it, somewhere down the line... but just think of it as a wacky rule of the game.

[hptroll]

"aap" is not related to "apne". That would be "aap" and "aapke".
Aapne refers to the subject of the sentence, no matter who that subject is (I, he, they, whatever).

[ambrasanta]

why in this time and not right now?

[JillRiepe]

I put 'Will you be in your room at this time?', but that is wrong because of the future sense, correct? Are you indicated that this time is right now.

[LinguisticBoi]

You are correct. It's wrong because of the future tense.