What is the difference between 때 and 에?

Question

What is the difference between these two sentences? 1 저녁에 봐요. 2 저녁때 봐요.

Are 때 and 에 interchangeable?

Answer 1

In here ~에 means at so see you at night ~때 in here means when so see you when night will sounds weird in English.

For example, 배고플때 is when you hungry, 슬플때 is when you sad

It is interchangeable sometimes but in my example it is not changeable.

Answer 2

The two things are definitely not interchangeable.

때 is a noun by formal grammar, but for convenience you can think of it as when or if (i.e. a conjunction) when it introduces a clause (by coming after it). For example:

심심할 때는 이거나 봐. (When you are bored, look at this--pointing to a book perhaps. 는 here suggests that boredom would probably not be the only condition for the whole time. 나 here suggests the book being offered is perhaps not a big deal.)

Or,

애가 심심해 할 때는 이거나 보여 줘. (When the child is/acts bored, show him this.)

For an example without 는,

빨간 불일 때 길을 건너다. (To cross the street when it is red light.)

When 때 introduces a substantive for an event or occasion, you can think of it as at, on, or about (i.e. a preposition), again just for convenience. For example:

• 회의 때 보다. (Lit. To see at the time of the conference, but meaning to see at the conference)
  
• 예배 때 보다. (To see at church service.)

I suspect this may ultimately come from:

• 회의 할 때 보다.
  
• 예배 볼 때 보다. (Here the first 볼 means to observe or attend.)

but have no basis to say so. Only, it might help you to relate the two constructions if you remember that "substantive + 때" and "substantive + verb + 때" convert to each other readily for the most part.

The exception to this convertibility would be things like 설 때 (around New Year's) or 방학 때 (during break from school).

To introduce a substantive for a time, use 에.

• 아침에 보다. (To see in the morning.)
  
• 오후에 보다. (Lit. To see between noon and midnight, but practically to see between noon and sundown.)
  
• 주말에 보다. (To see in the weekend.)
  
• 늦은 시간에 보다. (To see at a late hour.)

The following will all sound bad, in the respective senses above.

• 아침 때 보다.
  
• 오후 때 보다.
  
• 주말 때 보다.
  
• 늦은 시간 때 보다.

The only exception I can think of is:

저녁 때 보다. (To see in the evening.)

I.e. 저녁 as a reference to a time can take 때.

One complication arising from an ambiguity. 아침 and 점심 are not only a time, but also a meal, i.e. an event.

Therefore you can say the following in reference to the event.

아침 때 보다. (To see at breakfast, but not to see in the morning.)
점심 때 보다. (To see at lunch.)

In sum, 아침 때 and 점심 때 have only one usage, i.e. at breakfast or at lunch; but 저녁 때 has two, i.e. at supper or in the evening.

Again remember I did not say 때 was a conjunction or preposition; only that they might be a convenient comparison.