Typical ACH transfers takes 2-3 business days.
If you already hold investments/assets with Vanguard. Instead of sending the money to Vanguard first... Go directly to the BUY option. Pick your investment, the amount and then when you chose "Were is the money coming from" you pick the account. Vanguard will buy your investment, front you the money and give you that days price, pull the money out with the ACH transfer and your good to go.
If your funds fail, they sell the shares you bought and anything else they need to recover the costs.