Actually. Since it is bankshareable, the El Rewards. It would only take...
2 E.R per day. There is about 10 alts in one account. That's an automatic 20 E.R a day.
300/20 is 15. That's two weeks on farming, and not skipping a day.
That's not also mentioning that on the fifth day on each alt, you get an additional 3 E.R. That's 30 E.R on the fifth day + 100 E.R of accumulated E.R.
That's 130 E.R in under a week. Then comes the other two days. That's 170 E.R a week.
And don't forget to throw collected Fragments into Elysion tree for extra potential E.R. So in two weeks, or even under, you can get GOSCS.
Please check my math at your own interest. I could be wrong I just wrote an essay for school.