I tried to change my tomorrow's 11am flight to 1pm one. At 1:02pm, I called UA premier line for the change but the agent insisted a $150 change fee even though I'm a 1P and no differences in fare class. The agent was clueless but he reasoned maybe both segments need to be in the 24hr SDC window (the 1pm flight connects to a 3:30pm one). I hanged up, check in online, and saw the 1pm flight with the 3:30pm connection in the " Search Other Flight Options". I made the change, no charge.