I think with TDA it depends on your account type. I have an APEX account.

I am able to do an ACH deposit and trade the same day.. Did it this morning as an example. I had spent all my cash account balance last Friday on FITX. So at 8 am eastern I did an ACH deposit from my USAA checking account to my TDA account and bought 75,000 FITX on the first dip after opening today.

Call TDA and ask about what it would take to upgrade to an APEX account...