Available time-specific keywords in MF Connect for SyncCriteria

When defining Sync Criteria in MF Connect on DateTime-Fields, the following message is used as tooltip for Field Value:

So it seems that there exist some DateTime-dependent keywords.

But in the Documentation of MF Connect I didn't find a list of the available keywords.

Which keywords can be used in this place? 

I am looking for something like "Two Years Ago"

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