In the US, pre-market trading is from 4 am to 9:30 am EST and after hours trading is from 4 pm to 8 pm. on weekdays. Collectively this is called extended hours trading though some refer to both sessions as after hours trading.
Some brokers do not offer after hours trading. For those that do, it often requires that you get approval to do so, usually just a formality.
If your orders involved liquid securities, it's likely that either you don't have approval for after hours trading or that you didn't check the box that allows the order to be executed during extended hours trading.