If you have an account with a linked card, it shouldn’t take too long. If you want to buy BTC as fast as you can, link your bank card and fund the account with dollars. Keep them on the account until the right time to buy Bitcoins. It will be done instantly.
Even if you're bank card is not connected with your account, you can still buy Bitcoins within seconds if you have great savings. Not only capital is required to grab Bitcoins but the right time is also essential for buying Bitcoins at right price. Obviously it is going to cost you much more if you will go for Bitcoins during the pumping phase.