Ahh got it to work. I have to refresh the opened playlist. Then the imported dates are visible. If someone needs the export SQL from Media Monkey to Strawberry:
SELECT SongPath, Artist, Album, AlbumArtist, TrackNumber, DiscNumber, SongTitle, PlayCounter, strftime('%s', datetime(LastTimePlayed + 2415019.0)) as lastplayed
FROM Songs
WHERE LastTimePlayed > 0;
Media Monkey uses juliandate to save the date. I export the other fields additionally, to match the fields in Strawberry and find the correct songs. Form the returned entrys, i create the above UPDATE statement for Strawberry:
UPDATE `songs` SET `lastplayed` = 1631919400, `playcount` = 4 WHERE `artist` = "Some Artist" AND `album` = "Some album" AND `track` = 5 AND `title` = "some title";