Actually the "this month" isn't true any longer. Too much happened between Lorelai getting back and the wedding for it to be just 5 days, The wedding was moved because they decided to not comment on the election. They moved the date to right before the election. The Original date was November 19th
Rory started the book after she got back because Logan had reminded she said she needed to write the book. And she realized that even with Logan's continued offer of help she had to find herself. She had decided to take her life into her own hands. And then is hit with the curveball. And since Rory is just now deciding things 3 days before the wedding, it's safe to say she hadn't known she was pregnant long.
I think we are to assume that the LDB night was at the beginning of Fall and the Wedding around a month later. The change of seasons also makes Lorelai's coming back in November after only a few days away - off.
A month before November 5th fits Lorelai's timeline better imo.