I never waited 3 business days for Ameritrade when I electronic(ACH) deposit. Here is the secret... LOL
Do Electronic deposits before 5pm ET then log-in to Ameritrade again between 10pm and 1am ET then you will see the amount that you deposit. At same time, you will find that your fund is available for 'Non-marginable funds' as well :-) You need(MUST) make a 'buy order' that time otherwise you have to wait 3-days rule. Basically this deposit amount is available for you because the maintenance did not trigger yet.