Is a day trip worth it considering the travel time?

Yes, if you enjoy trains and want a change of scenery. You spend 5 hours total on the train, but the KTX is comfortable and productive for reading or planning.

Can I use my Seoul T-Money card in Busan?

Yes, T-Money cards work on all buses and subways in Busan. Just make sure it has enough balance before you leave Seoul.

Busan in a Day: A Practical Seoul-to-Busan Itinerary

To see Busan in a day from Seoul, take the earliest KTX train at 5:00 AM to maximize your time, as the journey takes 2.5 hours each way. Focus your visit on the coastal area between Haeundae and Gamcheon to minimize transit time and see the city's highlights without rushing.

Book your KTX tickets in advance. Use the Korail 'KorailTalk' app or website to book tickets at least 2 weeks out. Aim for the 05:00 or 05:30 AM departure to reach Busan by 08:00 AM.
Purchase a one-day subway pass. Upon arriving at Busan Station, buy a 'One-Day Pass' for 5,000 KRW at any subway station kiosk. It covers unlimited rides on the metro and is the most efficient way to get around.
Focus on two neighborhoods. Don't try to see the whole city. Stick to the Yeongdo/Gamcheon area in the morning and the Haeundae/Gwangalli beach area in the afternoon.
Catch the final return train. Book your return ticket for the 9:00 PM or 10:00 PM KTX. This gets you back to Seoul before midnight, ready for the next day.

Is a day trip worth it considering the travel time?: Yes, if you enjoy trains and want a change of scenery. You spend 5 hours total on the train, but the KTX is comfortable and productive for reading or planning.
Can I use my Seoul T-Money card in Busan?: Yes, T-Money cards work on all buses and subways in Busan. Just make sure it has enough balance before you leave Seoul.