Actually, I don’t think Schumer takes over until the GA senators are both 1) certified by GA, and then 2) sworn in to Senate; plus also no earlier than noon Jan 20th when Kamala becomes VP. Note GA certification may be delayed.The problem is doing that dumps it on Shumers lap. Shumer becomes majority leader the moment Harris is sworn in. Senate resumes session on the 19th, Shumer becomes Majority Leader on the 20th.
Certification could be as soon as the 15th at the earliest, but may be delayed to 22nd. State can’t certify until all counties complete certification. Fortunately, races ended up outside the 0.5% recount margin.