Nous jouons jusqu’à ce que le sablier soit vide.

Jusqu’à by itself is usually followed by a noun or a noun phrase:

• jusqu’à midi = until noon
• jusqu’à la fin = until the end

But here, what follows is a whole clause: le sablier soit vide.
French normally uses jusqu’à ce que when it means until followed by a subject + verb.

So:

• jusqu’à la fin = until the end
• jusqu’à ce que le sablier soit vide = until the hourglass is empty

Because jusqu’à ce que is one of the common French expressions that requires the subjunctive.

The verb être in the present subjunctive is:

• que je sois
• que tu sois
• qu’il/elle/on soit
• que nous soyons
• que vous soyez
• qu’ils/elles soient

So in jusqu’à ce que le sablier soit vide, soit is the correct subjunctive form for le sablier.

You cannot normally say jusqu’à ce que le sablier est vide.

In this sentence, the subjunctive does not add a dramatically different meaning in English. It is mainly there because French grammar requires it after jusqu’à ce que.

Very roughly, the subjunctive often appears after expressions involving:

• uncertainty
• emotion
• will
• possibility
• or an event that is anticipated rather than simply stated

Here, the idea is we keep playing up to the point when the hourglass becomes empty. French uses the subjunctive after until in this structure.

So the best way to learn this is:

• memorize jusqu’à ce que + subjunctive

Because vide here is an adjective, meaning empty, not a past participle meaning emptied.

So:

• le sablier est vide = the hourglass is empty
• le sablier est vidé = the hourglass has been emptied

In your sentence, the idea is the state of the hourglass: it is empty, so vide is correct.

Un sablier means an hourglass or sand timer.

It comes from sable = sand.

So:

• le sablier = the hourglass / sand timer

In this sentence, it is the object being used to measure how long the game continues.

Nous jouons is the present tense of jouer.

French often uses the present tense where English might say:

• we play
• we are playing
• or even something like we keep playing

So Nous jouons jusqu’à ce que... means something like:

• We play until...
• We keep playing until...
• We are playing until...

The future nous jouerons would mean we will play, which changes the time frame.

Yes. The French present tense is often broader than the English simple present.

Depending on context, Nous jouons can mean:

• We play
• We are playing
• We do play

So this sentence could describe:

• a general rule in a game: We play until the hourglass is empty
• something happening now: We’re playing until the hourglass is empty

Context tells you which one is intended.

Jusque is an older form, and in modern French it is usually used as jusqu’à before a noun or as part of set expressions.

Examples:

• jusqu’à demain = until tomorrow
• jusqu’à Paris = as far as Paris

Before ce que, it stays as jusqu’à ce que.

Also notice the spelling:

• jusque + à = jusqu’à

The apostrophe appears because à is a separate word beginning with a vowel.

Not really, at least not in the way you should think about it as a learner.

In jusqu’à ce que, the whole expression functions as a fixed conjunction meaning until before a clause. It is best learned as one chunk:

• jusqu’à ce que + subjunctive

So although ce que can mean what in other contexts, here it is part of the set phrase and should not be translated word-for-word.

No, not without changing the meaning.

• jusqu’à ce que = until
• avant que = before

Compare:

• Nous jouons jusqu’à ce que le sablier soit vide.
  = We play until the hourglass is empty.

• Nous jouons avant que le sablier soit vide.
  = We play before the hourglass is empty.

Also, avant que also takes the subjunctive, but it does not mean the same thing.

A careful approximate pronunciation is:

Noo zhoo-on zhus-kah suh kuh luh sa-blee-ay swah veed

A few helpful points:

• Nous jouons: the s in nous links to jouons, so you hear a z sound:
  nous-zjouons
• jusqu’à sounds like zhus-kah
• ce que is often said smoothly, almost like suh-kuh
• soit sounds like swah
• vide sounds like veed

Yes: learn it as a formula.

jusqu’à ce que + subject + subjunctive

Examples:

• J’attends jusqu’à ce qu’il arrive. = I wait until he arrives.
• Reste ici jusqu’à ce que je revienne. = Stay here until I come back.
• Nous jouons jusqu’à ce que le sablier soit vide. = We play until the hourglass is empty.

If you memorize the whole pattern instead of trying to build it from scratch each time, it becomes much easier.