Actually, Ethiopia wanted to fill the dam in 3 years and then agreed to fill it in 4 to 7 years. This is already agreed by Egypt and Sudan. The only thing left is the water flow during droughts i.e. who decides when a drought is and how can Ethiopia help Sudan and Egypt by releasing more water during drought. 10-12 years or even 20 years, that was first suggested by Egypt but is already off the table.
Why 3 years? Is that when the Dam constuction is scheduled finished?