What made Emerald think he could defeat the battle frontier in seven days?

[Pattyman]

I was kind of impressed to read about him trying to defeat seven leaders in seven days. This would have been normally impossible as there were bad guys (such as Guile Hideout) to deal with and it would have taken longer.

 

[Eitarou]

Except no one knew that Guile Hideout even existed at that point.

Unlike Ruby and Sapphire's challenge which consisted them going through the entire Hoenn Region, Emerald was on one small island with all of the Frontier Brains in one location.

 

[Kenshi]

That and Jirachi's one week among the conscious was (perhaps not-so) conveniently limited to that one week, and they had to squeeze in his challenges for the ultimate fate of climbing the Battle Tower and wishing the FRLG dex holders back to life. Since even holding Saque captive and telling her to restore their mobility wouldn't work, it was either Emerald won or the whole series gets thrown into disarray.