code: public static BigDecimal epoch(EvaluationContext ctx, Object datetime) {
          Instant instant = Conversions.toDateTime(datetime, ctx).toInstant();
          BigDecimal nanos = new BigDecimal(instant.getEpochSecond() * 1000000000 + instant.getNano());
          return nanos.divide(new BigDecimal(1000000000));
      }
docs: Converts the given date to the number of nanoseconds since January 1st, 1970 UTC