If I recall correctly it was 5-10 working days - I asked them via the chat function on the website and they told me. One of my jobs took 3 rounds of review to get it worded the way they wanted it, it was never longer than the timeframe they told me but it was always close to the max.
It looks like all versions of the Mechanical PE are still on the 2020 tentative timeline - so we've got a few years before it switches. I still think I'll try and pass the first run through though (here in 10 days).