They could have done it over 6-9 months. They chose to rush it by July 2nd after the TBAC target was published at the beginning of May.
This was communicated to the Fed, which was part of the reason Fed had to do 80(UST)+40(MBS)Bn QE every month
Fiscal stimulus: $80Bn per week
QE: $80+40Bn per month (Fed, 100% chance) + $160Bn per month (Treasury, 25% chance)