La réunion commence à dix heures moins le quart.

In French, à is the normal preposition used before a clock time.

So:

• à dix heures = at ten o’clock
• à neuf heures et demie = at half past nine
• à midi = at noon

In your sentence, La réunion commence à dix heures moins le quart, à means at.

Because French uses heure in the plural for most times other than exactly one o’clock.

• une heure = one o’clock / one hour
• deux heures = two o’clock
• dix heures = ten o’clock

So dix heures moins le quart is built from dix heures.

A useful comparison:

• Il est une heure = It’s one o’clock
• Il est deux heures = It’s two o’clock

Literally, moins le quart means minus a quarter.

French often tells time by counting backward from the next hour, just like English does in expressions such as quarter to ten.

So:

• dix heures moins le quart = ten o’clock minus a quarter
• natural English equivalent: quarter to ten

You may also see:

• moins cinq = five to
• moins dix = ten to
• moins vingt = twenty to

Examples:

• huit heures moins dix = 7:50
• onze heures moins cinq = 10:55

Because French normally says the quarter in this expression.

So the fixed pattern is:

• moins le quart = quarter to
• et quart = quarter past
• et demie / et demi = half past

Examples:

• neuf heures et quart = 9:15
• dix heures moins le quart = 9:45

You do not usually say moins quart in standard French.

Yes. That is another perfectly normal way to express the same time.

So these both mean 9:45:

• dix heures moins le quart
• neuf heures quarante-cinq

The difference is style:

• dix heures moins le quart is the quarter to ten style
• neuf heures quarante-cinq is the 9:45 style

Both are common. In everyday speech, many people use the digital-style version a lot, especially for clarity.

Because French, like English, uses the next hour after moins.

So dix heures moins le quart means:

• a quarter before ten
• therefore 9:45

It does not mean a quarter after ten.

Compare:

• dix heures et quart = 10:15
• dix heures moins le quart = 9:45

The key contrast is:

• et = past
• moins = to / before

Commence is the present tense of commencer.

• la réunion commence = the meeting starts / begins

French often uses the present tense to state schedules, timetables, and general facts, just as English does:

• Le train part à huit heures. = The train leaves at eight.
• Le cours commence à neuf heures. = The class starts at nine.

So commence here is very natural.

Yes. Réunion is a feminine noun, so it takes la.

• la réunion = the meeting

In French, nouns have grammatical gender, and you generally have to learn the gender with the noun.

That gender also affects adjectives and some other words later on. For example:

• une réunion importante
• la réunion est longue

A simple pronunciation guide is:

dee-zur mwuan luh kar

A bit more precisely:

• dix heures: the x in dix is pronounced like z before a vowel sound, so you hear a liaison: dee-zur
• moins sounds roughly like mwuan
• quart sounds like kar, with a French r

So the whole time phrase sounds approximately like:

dee-zur mwuan luh kar

One important point: the final consonants in French are often silent, but in dix heures, the x is heard because of the following vowel sound in heures.

In very informal spoken French, you may hear shortened time expressions, but for learners it is safer to keep heures.

So the standard, clear form is:

• à dix heures moins le quart

If you omit heures, it may sound casual or incomplete depending on context. In careful speech, classwork, or writing, use heures.

It is absolutely used in everyday French. Moins le quart is a normal, standard expression.

That said, modern spoken French also often uses the numeric style:

• neuf heures quarante-cinq

So both are common:

• La réunion commence à dix heures moins le quart.
• La réunion commence à neuf heures quarante-cinq.

Neither is wrong. The first sounds like quarter to ten; the second sounds like nine forty-five.

You might hear that in some contexts, but it is less precise if you want to talk about the starting time.

• La réunion commence à... clearly means the meeting starts at...
• La réunion est à... can sometimes be understood, but it is less idiomatic and can sound like a direct translation from English

More natural alternatives are:

• La réunion commence à...
• La réunion a lieu à... = The meeting takes place at...
• La réunion est prévue à... = The meeting is scheduled for...

So in your sentence, commence is the best choice if you mean the start time.

French simply organizes the idea differently.

English says:

• quarter to ten

French says:

• ten o’clock minus a quarter

So instead of using a word like to, French uses moins (minus / less).

This is just a different time-telling pattern:

• English: ten to eight
• French: huit heures moins dix

Once you get used to it, it becomes very natural.