Instructions for Form 9465
(Rev. December 2018)
Installment Agreement Request just state:
"You can choose the day of each month your payment is
due. This can be on or after the 1st of the month, but no
later than the 28th of the month.
When we approve your request, we will tell you the month
and day that your first payment is due.
If we haven’t replied by the date you chose for your first
payment, you can send the first payment to the Internal
Revenue Service Center at the address shown earlier that
applies to you."
Thus, you can mail a check if you prefer. Please see screenshots below.
For more information: https://www.irs.gov/pub/irs-pdf/i9465.pdf