When the time comes / on that occasion (届时)

Structure …（a future moment already mentioned）。届时 + 将/会 + announced event

届时 (jièshí) is an anaphoric adverb that points back to an already-mentioned future moment and announces what will happen then: "when the time comes", "on that occasion". It belongs to the language of announcements and official programmes (events, ceremonies, conferences), in written, formal register. It almost always leans on 将 or 会 for the future: 届时将举行庆典 = "a ceremony will be held when the time comes". It is not used for the present or the past: the reference point must be stated beforehand.

Examples

大dà会huì定dìng于yú下xià月yuè召zhào开kāi，届jiè时shí将jiāng邀yāo请qǐng各gè国guó代dài表biǎo出chū席xí。
The congress is set for next month; when the time comes, representatives from every country will be invited.
新xīn馆guǎn将jiāng于yú年nián底dǐ开kāi放fàng，届jiè时shí市shì民mín可kě免miǎn费fèi参cān观guān。
The new museum will open at year's end; when the time comes, citizens may visit it free of charge.
庆qìng典diǎn定dìng在zài国guó庆qìng当dāng天tiān，届jiè时shí全quán城chéng将jiāng燃rán放fàng烟yān花huā。
The celebration is set for the national holiday; when the time comes, the whole city will set off fireworks.

Levels are indicative: they follow the standard Chinese Grammar Wiki (AllSet Learning) progression, not an official HSK 3.0 mapping. We never assign levels by eye.

This point and the other 370, with audio on every example, inside Wanyu.