Penny stocks are considered non marginable..so there is a 3 business day waiting period after deposit..if you deposit Monday..funds won't be available until friday for trading.
There's a 3 day waiting period for stocks under 3 dollars if you deposit on line from your bank like I do to scottrade...(ST is changing to TD ameritrade maybe there different) ...to get the fund as quick as possible you'll have to deposit a check by hand to the brokers office...
From my personal experience and from what others have said etrade is best for penny stocks. Money available immediately most of the time with direct transfer from bank accounts.