Margin accounts that have lower Intraday futures margins will have the higher Overnight future margin requirements go into effect 15 minutes before the end of that future contract's designated Regular Trading Hours session.
You can keep track of the "Look Ahead Available Funds" and the "Look Ahead Next Change" in your Account Window's Available for Trading section (Click on the green "+" on the right to expand the section).
The Look Ahead Next Change time shows the time the Intraday and Overnight margins will change. The Look Ahead Available Funds includes any amount of the change in the margin requirement from Intraday to Overnight margins.
Please note, cash accounts and IRA accounts (both cash and margin type) are not afforded Intraday margin rates. MEXEM can rescind Intraday futures margins due to volatile trading conditions at any time without notice.
Additional information on when the Intraday future margin requirements start and end can be found on the MEXEM website.