Depends, if the shares you sold were purchased with cleared funds, most brokers will allow you to use the proceeds from the sale today immediately, however if you then sell the shares you purchase with the "unsettled money" before the original sale from today clears (before Thursday) you will get a good faith violation on your account. Which is more or less a slap on the wrist.
The thing you want to ask yourself is, if I buy tomorrow with these unsettled funds, am
I comfortable holding and not selling again for 3 days? Not that you can't sell- you can sell, you'll just get the violation
Who's your broker?