Please test Your local time server (pfsense) from windows machine. Is it synchronized to upstream servers at all? Stop windows time service, install ntpdate, and do test:
ntpdate -d yourlocalpfsenseserver
I think - better way for company's local time source - to use BSD "stock" ntpd from www.ntp.org, not OpenNTPD. Configure 3-5 reliable stratum1 or stratum2 time servers and keep Your windows machines always happy.
Arnis