Que tal usar um StartInterval de 2 semanas (1209600 segs)?
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
<key>Program</key>
<string>/scripts/autoSample</string>
<key>AbandonProcessGroup</key>
<true/>
<key>Debug</key>
<true/>
<key>StartInterval</key>
<integer>1209600</integer>
<key>Label</key>
<string>autoSample</string>
</dict>
</plist>