HPCC-9209 Add missing cast so max timing isn't truncated

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>
Merge pull request #4309 from ghalliday/issue9209

HPCC-9209 Add missing cast so max timing isn't truncated

Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>