As intraday requirements are set by the fcm they use the exchange minimum posting requirements assuming the position you opened will be held overnight. As saxon said, if oec's current day trade requirements are $500 you can carry 1 open position per $500/equity in your account.
However, be aware that intraday requirements, and for that matter exhcange requirements, can be changed at any time during periods of extreme volitility by your fcm or the exchange.
Additionally, the regular trading hours end at 3:15 pm cst. That's when overnight requirements take effect. No disrespect in the correction saxon as I know your posting was for illustrative purposes.