Se você tem GNU awk com mktime
function
awk '
FNR == NR{
d = mktime(gensub("[-:]", " ", "g", $2 FS $3))
if(D[$1] > d || ! D[$1])
D[$1] = d
next
}
{
d = substr($2, 1, 4) FS substr($2, 5, 2) FS substr($2, 7) " 0 0 0"
printf "%i %i\n", $1, (D[$1] - mktime(d)) / 86400
}
' file1 file2
produzirá
102 830
105 351
108 513