"When do they arrive?" can be used for future, but it can also imply we are expecting them now and how long do we have to wait. Someone could even answer, "They are arriving now." or "They should have arrived five minutes ago, but their flight has been delayed twenty minutes." or "The plane has arrived, but they are going through customs and that is taking longer than I thought. They'll be here soon."
"When will they arrive?" would be stated in French in the future tense. "Elles arriveront quand?" or "When are they going to arrive?" "Elles vont arriver quand?" Of course, I simplified by using the same form of question. "Quand arriveront-elles?" and "Quand vont-elles arriver?" are also valid as well as "Quand est-ce qu'elles arriveront?" and "Quand est-ce qu'elles vont arriver?"
My teachers (admittedly, I'm learning French in Northern Québec, so take THAT for what it's worth, haha) said the liaison should be more of a "z" sound. I was having a lot of trouble with the aural different between they have (ils ont) and they are (ils sont). They have is "eelz-ont" and they are is "eel-sont," softer and hissier. So my teachers would have said, "el-za-reeve."
Not at all arguing...just sharing. These discussions are helpful and amusing. Which is probably why I'm on here, and why my Rosetta Stone software and Tell Me More accounts were gathering dust for months before I found Duolingo.
No. I'd say "When do they arrive?" would be the usual query. I'd probably only say "They arrive when?" with a lot of emphasis on the last word, if, for example, my husband were to inform me that his 3 sisters, their husbands and children, were coming for a visit and they arrive in about half an hour. Ha.
I find the placement of "y" confusing. In a previous sentence, "quand est-ce que j'y arrive?", y was included. In this sentence, it's nowhere to be seen. Is the use of y with verbs like aller and arriver optional? Does it add anything important to a sentence like j'y vais (beyond the vague and redundant implication of somewhere)?