20 minutes further out for 100k less — worth it?

It matters, but not in the way the argument is usually framed. Do the calculation in hours rather than minutes.

20 minutes each way is 40 minutes a day, 200 minutes a week, roughly 3.3 hours. Over a ten-month program that is about 140 hours — three and a half working weeks. For 1,000,000 won saved.

So you are valuing your time at roughly 7,000 won an hour, which is below Korean minimum wage. On that basis alone, staying closer wins.

But the numbers are not the whole answer, and here is what actually decides it:

When the commute is fine:
- You get a seat. A 20-minute seated subway ride is usable time — vocabulary, reading, podcasts. Several students describe it as the most consistent study time they had.
- Your class starts at 1pm rather than 9am.
- The route is one line with no transfer.

When it is not fine:
- 9am class. Leaving at 08:00 instead of 08:30, five days a week, through a Korean winter, is the thing that quietly erodes attendance — and attendance is the one metric that affects your visa.
- Transfers. Two lines with a transfer is a different experience from 20 minutes on one line, even at the same total time.
- Standing. Rush hour on line 2 or 9 standing for 20 minutes is not usable time.

My actual advice: check the specific route on Naver Map with the departure time set to 08:15 on a weekday, and check whether you would get a seat by looking at where you are on the line. Two stops from the terminus is a seat; the middle of line 2 at 08:15 is not.

If it is one line, no transfer, and you would probably get a seat — take the cheaper room and use the time. If it is a transfer or standing room, pay the 100,000.