Learn Hardcore Russian: Днём я обычно работаю, а вечером отдыхаю. - In the daytime I usually work, and in the evening I rest.

So днём я обычно работаю literally means “by day I usually work”, but the natural English is “In the daytime I usually work” or “During the day I usually work.”
В день exists, but it usually means “per day” (e.g. два часа в день – two hours per day), not “in the day” as a time reference.

What case is днём exactly, and why does день change to дн-?

Днём is instrumental singular:

Nominative: день (day)
Instrumental: днём (by/with/at/in the day)

The change день → дн- is a stem alternation that happens in some Russian nouns. You just have to memorize that день has the stem дн- in oblique cases (дня, дню, днём, дне).

So днём is just the regular instrumental form of день, even though the stem looks a bit different.

Is вечером the same kind of form as днём?

Yes. Вечером is also instrumental singular:

Nominative: вечер (evening)
Instrumental: вечером (in the evening / by evening)

Just like днём, вечером answers “когда?” (when?):

Я работаю днём. – I work in the daytime.
Я отдыхаю вечером. – I rest in the evening.

So both днём and вечером are instrumental forms used adverbially to express time.

Why is there no в before днём and вечером? Can I say в днём or в вечером?

You must not say в днём or в вечером; those are ungrammatical.

For times of day, Russian normally uses the bare instrumental form without a preposition:

днём, утром, вечером, ночью

If you add в, you switch to a different case:

в день (accusative) – per day / on a specific day
в вечер is almost never used; instead you would say вечером or на вечер depending on meaning.

So:

✅ Днём я обычно работаю.
❌ В днём я обычно работаю.

Why is the conjunction а used instead of и or но?

А expresses a contrast or difference, often between two situations or times:

Днём я обычно работаю, а вечером отдыхаю.
→ During the day I usually work, whereas in the evening I rest.

Comparison:

и = “and” (simple addition, no contrast)
- Днём я работаю и вечером отдыхаю. – I work in the day and rest in the evening (just listing actions; less contrastive).
но = “but” (stronger opposition, often unexpected)
- Днём я обычно работаю, но сегодня отдыхаю. – I usually work in the day, but today I’m resting.

Here, а nicely shows a regular contrast between day and evening activities.

Why isn’t я repeated before отдыхаю?

In Russian, when two clauses share the same subject, it’s very common to omit the repeated subject in the second clause, especially when they’re connected by и / а / но.

So instead of:

Днём я обычно работаю, а вечером я отдыхаю.

you more naturally say:

Днём я обычно работаю, а вечером отдыхаю.

The я is understood from context. Repeating я is possible, but it sounds heavier and usually adds a slight emphasis, e.g. to contrast with someone else or another subject.

What does обычно do here, and where can it go in the sentence?

Обычно means “usually” and shows habitual action.

In this sentence, it modifies работаю:

Днём я обычно работаю… – During the day, I usually (as a rule) work…

Other common positions are:

Обычно днём я работаю.
Я обычно работаю днём.

All are correct; Russian adverbs like обычно are quite flexible. Differences are mostly about emphasis:

Обычно днём я работаю. – Emphasis on “As a rule, during the day I work…”
Я обычно работаю днём. – Emphasis on the habitual nature of working, with “днём” at the end.

Does the present tense here mean “I work” or “I am working”?

Russian present tense of imperfective verbs (like работать, отдыхать) covers both:

general/habitual meaning (“I work”)
ongoing action (“I am working”)

In this sentence, обычно (“usually”) clearly shows it’s about a habit:

я обычно работаю – I usually work / I work (as a rule)

If you wanted to stress right now, you’d use context words like сейчас:

Сейчас я работаю. – I’m working now.

Why is there a comma before а?

In Russian, when а connects two clauses (each with its own verb), you almost always put a comma before it.

Here we have two clauses:

(Я) обычно работаю – I usually work
(Я) отдыхаю – I rest

So you write:

Днём я обычно работаю, а вечером отдыхаю.

This follows the standard rule: coordinate clauses with а, но, да (in the sense “but”) are separated by a comma.

Can I change the word order, for example: Я обычно работаю днём, а отдыхаю вечером?

Yes, that’s perfectly correct:

Я обычно работаю днём, а отдыхаю вечером.

Russian word order is flexible. Common variants, all grammatical:

Днём я обычно работаю, а вечером отдыхаю.
Я обычно работаю днём, а вечером отдыхаю.
Обычно днём я работаю, а вечером отдыхаю.

Changes in word order mainly affect what is emphasized or what is presented as known vs. new information, but the basic meaning is the same.

I often see днем without the dots; is it the same as днём?

Yes. Днем (without dots) and днём (with dots) are the same word:

The correct spelling is with ё: днём.
In everyday writing, Russians often type е instead of ё, so you see днем.

Pronunciation stays [днём] with ё (like “nyom”). You should learn it as ё, but be ready to recognize it written as е.

How is днём pronounced? That дн cluster looks hard.

Днём is pronounced approximately:

[днʲом] – like dnyom in English.

Tips:

The дн is pronounced together, without an extra vowel.
The н is soft (palatalized) because of ё.
ё is stressed and sounds like English “yo” in “yoga,” but shorter: “nyom”.

So you can think of it as sounding close to “dnyom” in English transcription.