Edit: If a 3090 can get 4.8 GKey/s, then your numbers are pretty close...around 29-30 days!
Nono, i don't think so. A 3090 gets around 1500Mkey/s using Jean's Kangaroo. So half the time, maybe around 60 days. Still pretty a lot with a lot of electricity and GPUs to afford and to get. But it'll be worth the work in the end