This is not correct, as it pertains to the way most brokers are anyway. The initial margin is required in order to hold a position into the close, not to trade after "day session" hours.
For example, if I buy an ES contract at 6:01pm ET, most brokers will only require the day trading margin for that contract (usually between $400 and $1000). However, if I buy at 4:14pm and wish to hold through the close, then at the close I must have $3850 per open contract.
Once into the beginning of the new session after 6:00pm, the margin requirement goes back to day trading levels (for most brokers anyway--I have seen one that only extends day trading margins starting at 8am, instead of the prior open at 6pm). The exchange requires the account to meet the margin at the settlement, which is when business is concluded and this ensures that any open positions are properly backed.
The period when the exchange is closed is where the real risk is, as open positions are sitting ducks in the event of a catastrophe. During this time, the broker is not willing to accept this risk, so he requires the account holder to fully meet the margin himself. However, during any other time when the market is open, there is no real risk to the broker in extending the additional capital to meet the exchange requirement, as he can simply close the position if margin limits are exceeded.
This is my understanding, and a similar "correct me if I'm wrong" is applicable here as well.
So with this in mind, if a firm requires a trader to be flat before the close, the trader could accomplish the same exact thing by having the $300-$500 day trading margin requirement that most brokers offer per contract traded. I'm not advocating utilizing this level of margin in any way, just saying what is standard in the industry. Since TST's "$30K account" allows 3 contracts max that must not be held into the close, an equivalent personal account that meets the same risk parameters would be about $1500-$2000. For the "$150K account", max size 15, using ES again, with the same parameters TST uses the actual account size would only have to be less than $10,000. There is not a "$30K account" and if there were, it would be a poor allocation of funds (to sit in an account where only about $11,000, or 40% of it, would be actually needed for true margin, or $2000 for intraday margin). It would be like depositing $5K in a bank and putting the other $25K under your mattress. I like TST and would recommend it to anyone trying to learn trading or improve their trading, and I used it for that very purpose, but anyone who thinks they offer a "$30K account" simply does not understand the math behind the model. They fund traders, but not nearly with the amount specified given the risk parameters that are in place.