Fix duplicate apply_time field SQL error in DB.

When we do a few little megration (less than 1 sec long), we get the duplicate values error in the 'apply_time' field.
I think the change of timeformat (accurate to the microseconds) would solve this problem. But not to break backward compatibility I suggest to do "sleep(1)" for 1 
second during the any mergation up process. 
In this case the timestamp would be different.