A trading period always start on a Wednesday and continues through the following Monday. It is possible to place stock orders on any day during the trading period, but the order depth (presentation of all buyers' and sellers' orders) is only updated between 10 am and 4 pm.
The companies listed at Alternativa Listan are generally traded monthly, while most of the companies listed on the Pepins Market are traded quarterly (in March, June, September, and December).