Learn Hardcore Korean: jihacheori jiyeondwaeseo chulbal sigani neujeul geos gatayo. - The subway is delayed, so the departure time will probably be late.

지연되다 means “to be delayed.” The form 지연돼서 is a contraction of 지연되어서, where -여서/어서 attaches to the verb to indicate cause. So 지연돼서 literally means “because (it) is delayed.”

Why is the connective -서 (in 지연돼서) used instead of simply ending the clause?

In Korean, -아서/어서 (-서) is used to link two clauses when the first clause provides the reason or cause for the second. Here, 지연돼서 explains why the departure time will be late.

What nuance does -을 것 같다 add to 늦을 것 같아요?

-을 것 같다 attaches to the future or present attributive form of a verb to express an assumption or likelihood. 늦을 것 같아요 doesn’t state a fact; it means “it seems like it will be late” or “I think it’ll be late.”

Why do we change 늦다 to 늦을 before 것 같다?

When you use -을 것 같다, you need the verb in its future attributive form (verb stem + 을/ㄹ) before 것. For 늦다, you add 을 (since the stem ends in a consonant), yielding 늦을 것 같다.

What does 출발 시간이 mean, and why include 시간?

출발 means “departure.” Adding 시간 (“time”)—출발 시간—specifies “the departure time.” It’s more precise than just 출발 and clarifies you’re talking about the schedule.

What politeness level is indicated by the ending -아요 in 늦을 것 같아요?

The -아요/어요 ending is the informal polite style (해요체). You’d use it in everyday conversation with colleagues, acquaintances, or customers—not with close friends or family (where you might use the plain style), and not in formal speeches (where you’d use 합니다체).

Can I make this sentence more formal? How?

Yes. In formal polite speech (합니다체), you could say:
지하철이 지연되어 출발 시간이 늦을 것 같습니다.
Here, -되어 is the full form of 돼서, and -것 같습니다 raises the politeness level.