timeline problems in "Northwest Mansion Mystery"
#1:
In the teaser it is said to be 24 hours before the big party starts. After Ptolergeist activity Mr. Northwest decides Dipper is the one to exorcise the ghost.
But the tv news coverage says the party will be tonight just before Pacifica arrives to ask Dipper. When they arrive back at the mansion Mr. Northwest says it is an hour before the guests arrive. Thus 23 hours - minus the time it took the travel back and forth and the time it took for Dipper and Mabel and her friends to get ready - have elapsed since Preston Northwest decided to get Dipper.
What happened in the probably more than 20 hours before Pacifica left the mansion to get Dipper? Did Preston Northwest call the Mystery Shack several times only to be ignored because the phones had caller identification, and then decide to send Pacifica in person as a last resort?
#2:
The ghost mentions 150 years twice in his account.
He says that the Northwests asked the lumberjacks to build a mansion at the top of the hill 150 years ago to the day. Since Gravity Falls is set in the summer of 2012, that must have been in the summer of 1862.
The Lumber ghost says that it took years to build the Northwest mansion. After it was finished the townsfolk arrived for the first annual party they had been promised but were locked out. With his dying breath the ghost said that he would take bloody vengeance if the Northwests did not let the townsfolk in to party 150 years in the future.
Thus the confused story told by the ghost seems to imply that the episode is exactly 150 years to the day after two separate events which were years apart.
Possibly one of the writers calculated that the summer of 2012 would be 150 years after building started in the summer of 1862 and another writer calculated that 2015 would be 150 years after 1865 and thus there could be up to three years between the starting and the completion of the mansion, without realizing that the second season of Gravity Falls has a fictional date of 2012 and not 2015.