org.apache.cassandra.db.marshal.TimestampType.dateStringToTimestamp() contains a regular expression that checks to see if the String argument contains a number. If so it parses it as a long timestamp. However pre-epoch timestamps are negative and the code doesn't account for this so it tries to parse it as a formatted Date. A tweak to the regular expression in TimestampType.dateStringToTimestamp() would solve this issue.
I could use formatted date strings instead, but the TimestampType date parser uses ISO8601 patterns which would cause the timestamp to be rounded to the nearest second.
Currently I get the following exception message:
unable to coerce '-86400000' to a formatted date (long)