Initial thought was to use Mac's launchd as described at developer.apple.com but somehow I could not get it working :-(
So I got onto my unix comfort zone; so to use crond. There I have a script at ~/bin/iSync.scpt which contents as
tell application "iSync"and a cron job added using "crontab -e" as below
if not syncing then exit repeat
and seems to work just fine.
#m h dom mon dow command
25 16 * * 1-5 osascript ~/bin/iSync.scpt