Learn Hardcore Japanese: watasi ha daitai sitizi ni eki ni tukimasu.

Both meanings exist, but here it means approximately because it comes right before 七時. So it’s “around seven.”
If you want “usually,” use たいてい or ふつう:

たいてい七時に駅に着きます。 = I usually arrive at 7.
（だいたい ≈ generally） is possible in some contexts, but for habits たいてい is the more natural choice.

Can I say 七時ごろ or 七時くらい instead of だいたい七時? Do I need に after them?

Yes.

七時ごろ（に）: ごろ is “around (time).” The に is optional after ごろ; both are common.
七時くらいに: くらい also means “around,” but with times it’s safer to include に. (Casually some people drop it, but keep に in careful speech/writing.) All of these are natural: だいたい七時に／七時ごろ（に）／七時くらいに.

Why are there two に’s in the sentence? Are they the same particle?

Yes, it’s the same particle used for two roles:

七時に: に marks a point in time.
駅に: に marks the arrival/destination with 着く. It’s normal to have multiple に’s when you have both a time and a destination.

Why is it 駅に着きます and not 駅で着きます? Can I use へ?

着く takes に for the place you arrive at.
で marks where an action happens (e.g., 駅で待ちます “I wait at the station”), not the arrival point.
へ with 着く is rare and sounds old-fashioned or stiff. In modern everyday Japanese, use 駅に着きます.
(Use 駅へ行きます “I go to the station” with 行く, where へ is fine.)

Is 私は necessary? Can I drop it?

You can drop it if context makes the subject clear.
だいたい七時に駅に着きます。 is perfectly natural. Japanese often omits pronouns.

Why は after 私 and not が?

は marks the topic: “As for me, …” It’s the default in neutral statements about yourself.
が marks the grammatical subject and often adds focus/contrast: 私が七時に駅に着きます can imply “It’s me (not someone else) who arrives at 7.”
So 私は… is the ordinary choice here.

Why is the verb non-past (着きます) when I’m talking about a habit or future schedule?

Japanese non-past covers present, future, and habitual actions. Adverbs and context supply the nuance. Here, だいたい + a clock time makes it a habitual statement (“I usually/roughly arrive around 7”).

Can I change the word order? For example, 駅に七時に着きます or 七時に駅に着きます? Where should だいたい go?

Typical order is Topic → Time → Place → Verb. So 七時に駅に着きます is the most common.
駅に七時に着きます is also grammatical but less typical.
Put だいたい immediately before what it modifies:
- Approximate time: だいたい七時に… / 七時だいたいに… (the first is more natural)
- If you mean “generally/mostly (I arrive at 7)”, prefer たいてい: たいてい七時に駅に着きます。

How do you pronounce 七時? Is it しちじ or ななじ?

Standard is しちじ (shichiji). Some people say ななじ informally to avoid confusion with いちじ (1 o’clock), but しちじ is the textbook/careful form.

How do you read 着きます, and how do I avoid confusing it with 来ます or 着ます (to wear)?

着きます (to arrive) is read つきます. Dictionary form: 着く（つく）.
来ます (to come) is きます. Dictionary form: 来る（くる）.
着ます (to wear) is also きます. Dictionary form: 着る（きる）. Watch for the extra き after the kanji in 着きます (つきます) versus 着ます (きます).

Is 着く transitive? Can I say 駅を着きます?

着く is intransitive, so you cannot use を for the destination. Use に:

Correct: 駅に着きます。
Incorrect: 駅を着きます。

Is だいたい七時ごろ okay, or is that redundant?

It’s a bit redundant (two “around” markers), but people do say it in casual speech for emphasis or looseness. In careful speech/writing, use just one: 七時ごろ（に） or だいたい七時に.

Can I use 約 or およそ instead of だいたい?

Yes, but they’re more formal/literary:

約七時に駅に着きます。
およそ七時に駅に着きます。
In everyday conversation, 七時ごろ or だいたい七時 sounds more natural.

What’s the difference between 着く and 到着する?

着く is everyday and natural in conversation.
到着する is formal/politer (announcements, reports).
E.g., a train announcement might say 七時に到着します, while you’d normally say 七時に着きます.

Do I always need に after time words? What about 今日 or 明日?

For exact clock times like 七時, use に: 七時に.
For relative days like 今日／明日／毎日, に is usually omitted: 明日駅に着きます (not usually 明日に).
For days/dates (e.g., 金曜日, 3月10日), に is optional.

What happens if I say 駅には instead of 駅に?

駅には七時に着きます topicalizes/contrasts the station: “As for the station, I arrive at 7 (as opposed to somewhere else at a different time).” It implies contrast or sets up comparison (e.g., 会社には八時に着きます). Use plain 駅に when no contrast is intended.

Politeness: when do I use 着きます vs. 着く?

着きます: polite style (neutral/respectful, with strangers, in formal contexts).
着く: plain/casual (friends, diaries, informal messages).