Rain changes the walk between Daegu's sights as much as the visit itself. Choose one indoor anchor, check its opening day and route, then keep the next stop close enough that a wet transfer does not take over the day.
Daegu National Museum has fixed visitor limits
The museum at 321 Cheongho-ro, Suseong-gu is open 09:00-18:00, with admission ending 30 minutes before closing. It closes Mondays, New Year's Day, Seollal and Chuseok; if Monday is a public holiday, the next non-holiday weekday is the closure day. General admission is free, although special exhibitions may charge. From Manchon Station on Line 2, use Exit 3 and transfer to a city bus; free parking is available but limited.
Use Seomun Market only after checking the stalls you want
The market's listed daytime hours are 09:00-18:00, but individual shops vary and the first and third Sundays are market closure days. The night market is a separate evening operation; its official schedule is Friday and Saturday 19:00-23:30 and Sunday 19:00-22:30, with weather-related changes possible. A market listing does not guarantee a particular food stall is open.
Make the transfer the deciding factor
The museum is in Suseong-gu while Seomun Market is in Jung-gu. Do not add both automatically: check the live bus or metro route and leave enough time to arrive before the museum's last admission. If the rain is heavy, keep the museum as the main visit and choose a meal nearby instead.