This post will be updated, but for the mean time this should work:
find . -maxdepth 2 -type d -exec stat -c "%y %n" {} \; | sort | tail -n 20
Update 1:
This is much faster:
find . -maxdepth 2 -type d -printf "%TY-%Tm-%Td %TH:%TM:%TS %TZ %p\n" | sort | tail -n 20
🙂