It's one syllable. The OP in this case is actually being misguided by zhuyin, and would be better served by pinyin. With his poor understanding of the rules of

It's one syllable. The OP in this case is actually being misguided by zhuyin, and would be better served by pinyin. With his poor understanding of the rules of how sounds in Chinese combine in real speech, it looks to him like two syllables, but it's not, because sounds combine in practice. Or... maybe he's thinking of Chinese opera. Yeah sure when listening to Chinese opera, all kinds of sounds get lengthened into many syllables ;-). But really I can imagine how this happened. Couple of IPA wonks sit down with a Chinese native speaker, maybe a linguist, and they say, wtf, explain to us what is the difference between 'jun' and 'zhun'? The Chinese person does a hyper-exaggerated slow demonstration of the sounds, and they write that down as the official IPA transliteration that the OP is fixated on, further cementing a misunderstanding of real usage that was implied by the zhuyin transliteration. As to Xi'an, pinyin has a rule for that kind of case, which is to add an apostrophe in between the parts to resolve the ambiguity.