TKU - RIX departs at 18:40 and returns at 21:20 on Wednesday and Sunday.
GDN - TKU currently arrives at 18:10 and leaves at 18:40 on Mon, Wed, Fri and Sun. So I'd expect the Gdansk aircraft to go off to Riga on Wednesdays and Sundays, and for the TKU - GDN flights on those days to be retimed to 21:50.