Time expressions and 'at' に
Telling time in Japanese is mostly attaching pieces to numbers you already know: じ for the hour, はん for half past, ようび for days of the week, がつ for months. The one new grammar piece is the particle に, which marks a point in time — 'at 7', 'on Monday'. As a rule of thumb: if you'd say 'at' or 'on' in English, に in Japanese.
Today, tomorrow, yesterday, now
きょう = today (kanji 今日 — irregular, learned as a chunk). あした = tomorrow. きのう = yesterday. いま = now (kanji 今 — same character as in 今日). These four cover most everyday timing without any particle: きょう、しごと です。 = 'Today, (it's) work.' Add a verb you already know: きのう、ほん を よみました would say 'Yesterday I read a book.'
Days of the week
All seven end in ようび ('day'): げつようび (Mon, 'moon-day'), かようび (Tue, 'fire'), すいようび (Wed, 'water'), もくようび (Thu, 'tree'), きんようび (Fri, 'gold'), どようび (Sat, 'earth'), にちようび (Sun, 'sun'). To ask: なんようび です か。 = 'what day is it?' Reply: げつようび です。
Months — just a number + がつ
Months are numbered. Add がつ to a number 1–12: いちがつ (January), にがつ (Feb), さんがつ (Mar)… じゅうにがつ (Dec). Three irregulars to memorize: しがつ (April — uses し, not よん), しちがつ (July — uses しち, not なな), くがつ (September — uses く, not きゅう). To ask: なんがつ です か。 = 'what month is it?'
Dates 1–10 — the bumpy bit
Dates 1–10 use special readings, not the regular numbers: ついたち (1st), ふつか (2nd), みっか (3rd), よっか (4th), いつか (5th), むいか (6th), なのか (7th), ようか (8th), ここのか (9th), とおか (10th). From 11 on, they regularize: じゅういちにち, じゅうににち… with にち ('day'). One more exception: はつか = the 20th. Yes, dates are the worst part of A1 Japanese — but you'll hear them everywhere, so it's worth meeting them now.
Telling time — じ and はん
Hour = number + じ: いちじ (1 o'clock), にじ (2), さんじ (3), … じゅうにじ (12). Three irregulars: よじ (4 o'clock — uses よ, not よん or し), しちじ (7), くじ (9). 'Half past' = はん: しちじ はん = 7:30. To ask: いま なんじ です か。 = 'what time is it now?' Reply: さんじ です。 = 'It's 3.'
に — 'at a time' / 'on a day'
When you mention a clock time, a day, or a date with a verb, attach に after it. しちじ に おきます。 = 'I get up at 7.' げつようび に いきます。 = 'I go on Monday.' But — and this is the trick — きょう, あした, きのう, いま never take に: just きょう、いきます。 Context-relative time words skip the particle.
