We had to find a way, for a Swedish PPM client, to automatically synchronise a Portfolio through GEL, because once the synchronisation is done we had to launch a second process that would perform a few more actions.
That's when i learned that there's a very easy way to do that using the syncschedule_cron tag in a Portfolio XOG.
Using the format: syncschedule_cron = minute hour day month *
<NikuDataBus xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="../xsd/nikuxog_pfm_portfolio.xsd">
<Header action="write" externalSource="NIKU" objectType="pfm_portfolio" version="18.104.22.1688"/>
<pfmPortfolio syncschedule_cron="00 12 18 09 *" code="PFM_000001" currency_code="EUR" name="My Portfolio">
This will synchronise this portfolio at 12:00 on 18th of september.
Hope that helps someone with the same problem