When I looked at it a couple of years ago I found that TDA, which I use, promoted this 24/5 but didn't really deliver.
First, TDA has more than one platform and it's not clear that this would apply globally. For example, the Singapore based platform requires selling lots in FIFO order while the US platform is flexible.
Then, and it's detailed in the article, the 24/5 is limited to a list of ETFs, so not all stocks.
Finally, TDA does not operate from 4 am to 8 pm as stated, they operate from 7 am to 8 pm EST.
I've said it before, but I find it incredible that in a world of 24/7 supermarkets or gyms, trading is restricted to union hours (9:30 am to 4:00 pm...seriously?).
The mecca of supply and demand should be open 24/7/365 and the brokers that will be first to come close will be the kings of the world.
The CEO speaks of limited volume as the reason for their limited hours, but I don't buy it. Traders are conforming to the hours they are given. Expand the hours and suddenly traders find other things to do with their day and trade when they find it more convenient to them and not the system. Open the times gate and they will come, from Europe and Asia, in far greater numbers than the CEO can even fathom.
But maybe that's precisely the reason the gates are controlled? Imagine if the best trading happens at 3 am EST?