You are right that Christians use Matt. 24:36 as an excuse not to look for the time of our Lord's coming for us.
 
Irony of all ironies is this........verse 36 is talking about verse 35 and has absolutely nothing whatsoever to do with a rapture, zero, nada!
 
Jesus said in verse 35; heaven and earth will pass away, but my Words will not pass away.  BUT OF THAT DAY (when heaven and earth passes away) knoweth no man, no not the angels in heaven.
 
When will heaven and earth pass away? At the end of the 1000 year millennium reign, so at this point there is no reason on earth that we need to know about that event.  That was the message Jesus was trying to get across.  Has absolutely nothing to do with a rapture.
 
Why doesn't the church catch on to this very simple statement? Because verse 36  is taken out of context and has become a doctrine of error that the church has swallowed hook, line, and sinker.
 
God bless.
 
Webster