とけい
Where し, しち and く finally earn their keep

4, 7 and 9 o'clock take し-family readings. There is no alternative — よんじ isn't a thing.
4:00 = よじ
ふん becomes ぷん after 1, 3, 4, 6, 8 and 10 — the same rule as 〜ほん.
3分 = さんぷん
A clock time takes に. きょう, あした and いま never do — they aren't points on a clock.
ろくじに おきます

いま よんじ… ですか?

よじ です。 この みっつだけは かわりません。
〜じ
Unit 57 said し・しち・く were locked into certain phrases and that clock times were one of them. Here they are. Nine of the twelve hours are just the number plus じ; the other three have no alternative reading. 🔊 Tap any row.
With plain numbers you could pick either reading. Here you can't. よじ・しちじ・くじ are the only forms anyone says — よんじ and きゅうじ will simply be heard as a mistake. And notice 4 o'clock is よじ, not しじ: the し reading loses its consonant here, which is why this hour catches people twice.
〜ふん・〜ぷん
You already know this rule. ふん becomes ぷん after 1, 3, 4, 6, 8 and 10 — exactly the softening that turned ほん into ぽん in Unit 58. Learning counters was learning this.
Half past is はん, not さんじゅっぷん. Both are correct, but はん is what gets said — the same way English says “half seven” rather than “seven thirty” when it can.
じかんを いう
Hours then minutes, in the order the digits are written. The one thing that moves is ごぜん and ごご: English puts a.m. and p.m. at the end, Japanese puts them in front.
Hours first, then minutes — the same order the digits are written in. はん replaces さんじゅっぷん and is what people actually say. ごぜん and ごご go in FRONT, unlike English “a.m.” and “p.m.”, and Japanese uses a 12-hour clock in speech.
Asking is the same trick as いくつ in Unit 58 — put the question word where the answer would go.
Swap the time for なんじ and leave everything else alone — the same trick as いくつ in Unit 58. One thing to watch: に attaches to a CLOCK time but never to きょう, あした or いま, because those don't name a point on a clock. 〜ごろ means “around”, and it replaces に rather than joining it: しちじごろ, never しちじごろに.
かいわ
Four exchanges. Read the question, say your answer out loud, then check.

いま なんじ ですか。
What time is it now?

よじ はん です。
It's half past four.

まいあさ なんじ に おきますか。
What time do you get up every morning?

ろくじ じゅうごふん に おきます。
I get up at 6:15.

しけんは なんじ に はじまりますか。
What time does the exam start?

ごぜん くじ に はじまります。
It starts at 9 a.m.

ばん、なんじごろ ねますか。
About what time do you go to bed in the evening?

じゅうにじごろ ねます。
Around twelve.
クイズ
Twelve questions. The three fixed hours and the six minute changes are where the marks are — the wrong choices are the readings people actually reach for.
Question 1 / 12 · 0 correct