Hi Sevenson,

Well, 一会 means "a little while" or "a short time". In northeastern colloquial dialects, particularly Beijing dialect, "儿" is tacked on to the end of some words to... I dunno, give them flavor? It doesn't change the meaning. So, 一会儿 still means "a little while". 不一会儿 means "Not long after", or literally "It wasn't a little while" [before something happened]. Make sense? 

Glad you enjoy the site! If you ever have a short passage you'd like translated, do submit!