$ cat filename && ./t.awk
7  65  2    5   32070  2010-12-14    13:25:30
7  82  2    10  41920  2010-12-14    11:30:45
7  83  1    67  29446  2010-12-14    04:15:25
7  81  1    47  32070  2011-5-11      08:14:20
7  83  1    67  29446  2011-6-22      07:13:24
7  82  2    10  41920  2011-5-14      06:15:25
7  82  2    10  41921  2011-5-14      06:15:25

7  65  2    5   32070  2010-12-14    13:25:30   147
7  82  2    10  41920  2010-12-14    11:30:45 150
7  83  1    67  29446  2010-12-14    04:15:25   189
7  81  1    47  32070  2011-5-11      08:14:20 147
7  83  1    67  29446  2011-6-22      07:13:24     189
7  82  2    10  41920  2011-5-14      06:15:25 150
7  82  2    10  41921  2011-5-14      06:15:25 -1

# 7  82  2    10  41920  2011-5-14      06:15:25


awk '{
       split($6,arr,"-")
       a=sprintf("%s %s %s 0 0 0",arr[1], arr[2], arr[3])
       d=mktime(a)
       # this is to handle the fact that you want the same data early and late 
       # in the output
       delta[$5]=delta[$5] " " d
     } 
     END {for(i in delta) {print i, delta[i]}  }'  filename > tmp.dat

#    
# display output, print error "-1" if each $5 does not occur twice in the input file
awk '{
      if (FILENAME=="tmp.dat" )
      { 
        delta[$1]=$0; 
        next
      }
      if (FILENAME=="filename")
      { 
        a="-1"  # default is error
        if($5 in delta)
        {
           cnt=split(delta[$5],arr)
           if(cnt==3) # correct number, 1 for $5 two & three are epoch seconds
           {
             a=arr[3] - arr[2]
             a/=86400
             a=int(a)
           }
        }
        print $0, a      
        next
      }
    }' tmp.dat filename   
# note the order of files here is important