Quote from ScalperJoe:
Excellent post, and it's important to understand the concept of "settled" cash balance. If you buy a security using your cash balance in a retail account and hold overnight, you CANNOT "churn" the cash once that security is sold due to Reg T rules, which makes you wait for "T+3" (trade day plus three days) in order for the cash to become settled.
Not exactly.
The Reg T rules you're referring to only apply to a cash account. If you close a trade that hasn't settled yet and you've not deposited the Reg T minimum to cover the trade you're freeriding and end up with an account that's frozen for 90 days.
However, once the trade settles (or you've deposited funds) you can sell stock from a settled trade and use those proceeds to create another position during the same day.
But, those Reg T rules do not apply to a margin account unless the broker, who's free to implement more restrictive margin rules than Reg T, has done so.