You can trade assets only during market hours:
Normal market hours (also called trading session) are 8:30 am CT to 3:00 pm CT + pre- and post-trade market hours. Trading before and after hours has an additional cost.
Market half-day days occur before or after certain holidays and vary depending on the asset type in your order. For stocks and mutual funds, market half-day days are 8:30 a.m. CT to 12:00 p.m. CT. For fixed income securities, market half shifts are from 8:30 am CT to 1 pm CT.