when to pay quarterly taxes

The IRS requires payments 4 times a year and provides a deadline to make those payments, however, you are able to make additional payments if that is easier for you to manage.  The goal is spread your tax payments out over the course of the year, rather than having a large balance due at filing.    Another thing worth noting is that your estimated payment are not required to be equal.  If your income varies throughout the year (for example, you have a small retail business and make more money during the last quarter due to holidays sales,) you can make larger payments when you have more taxable income generating a tax liability.  

Be cautious if you do make more than the 4 required estimated tax payments that you keep excellent records.   This is also true if you payments are not the same for each quarter.  There is a process to report when your income was earned in relation to those estimated payments if they are varied due to the timing of your income. 

When it's time to file you will need to be able to identify how much you paid and what date the amount was paid on.  When entering the information in TurboTax, you are able to enter multiple payments that occurred within each estimated tax payment period - just make sure you have those details saved somewhere that you can find them when you are ready to file your return.