Jesus said He would return at a time "we think not."  However...He may not have been referring to a certain period such as Pentecost, Tabernacles, what have you.

Think about it.  Even the most ardent watcher gets involved in their daily activities of family, work, school, etc.  There are many times during the day when I "think not" because of pre-occupation with daily life.  I'm sure others are likewise.

Even on days when I am particularly paying attention, those moments of "think not" occur.  So even if one thinks they know, He'll probably still arrive at a time when they are thinking not.  

Just a thought

Ed C