The SoS had a ton of discretion in the case, the judge actually gave him a chance to propose an amended calendar that complied with the law but his only idea was "derp let's allow people to keep sending in ballots after we count all the votes"
Propose something that complies with Georgia statute and the Federal law at the same time in this scenario if the legislature doesn't act if you are the SoS.
The 28-day state law runoff requirement is a hard date for state races. The 45-day minimum absentee ballot federal law requirement is a requirement in the Federal races. The only way out of the box is for the legislature to rewrite the law to mirror the Federal requirements. Otherwise you are stuck with two runoffs.
And if turnout wasn't THE key to winning the runoff, do you really believe the leg wouldn't have readily changed said law?