After testing with the ACE Pilot software, we found that the em620 LoadProfile1 has a status column that gives you a powerdown event if it occured in the specific profile period, with a description 'PowerDown' and the profile row timestamp as the start time of the event. Then in the StandardEventLog, we get PowerUp entries, with the event timestamp as the end of the event.
After implementation we were having a hard time getting the event start and end dates to line up and after taking a closer look, we realised that the both timestamps in the LoadProfile1 and StandardEventLog are within a few seconds of eachother, with a gap in the profile before the supposed 'PowerDown' event.
This leads to the conclusion that the timestamps are actually the time when the power came back on, after the outage, so it is not possible to accurately gauge the exact time that the powerdown occured.
For this reason we log the powerUp event, read from the meter's StandardEventLog, and log it as an instantaneous event.