Is using the resultative complement 到 generally equivalent to saying "at the time this action was finished"?
Yes, you can think of it that way, but not in the example you've provided.
If you want to use in that sense, 到 would be paired with 了, signifying "an end", or "in the past".
Without the 了, "我到北京" would give no indication of time.
到 as a definitive destination identifier.
到 here is identifying a set location for you to travel to.
As for your example sentence:
Can 你走到车站的时候已经很晚了吗？ be translated as "By the time you reached the station were you already late?"
You are correct that "晚" does mean "late", but moreso as a time of day. You can use 迟到 (Chí - "late, tardy, slow" Dào - "until", "arrive") to describe "being late for something", or "to arrive late".
Or, you can use 来得及 （Lái de jí- "in time for"）and 来不及 ("not in time for") to describe situations where you were your lateness actually caused you to miss something.
你来得及到火车站了， 让你刚好 (Gāng hǎo - "just", "happen to be")上火车了
You just made it to the train station on time, allowing you to just make your train
You arrived too late to the train station, so you missed your train!
For a general purpose word to describe "at this time this action was finished", you can use 完 (Wán - "complete"), or even 好.
我吃完了 - "I finished eating"
你完蛋了 - "You are finished (you are screwed)"
我做好功课了 - "I finished my homework"