If you look at the example I linked to, they use the $$NOW variable instead, I tested this locally and it seemed to work:
mongoexport --db Cinema --collection Cinemas --fields field1 --query "{ \"$expr\": {\"$gt\": [ \"$createdAt\" , {\"$dateSubtract\": {\"startDate\": \"$$NOW\", \"unit\": \"day\", \"amount\": 1}}]}}" --out output.csv
Obviously you’ll need to update the query to suit your needs as I just took 1 day off the current date