However, to your particular point, why are you doing this? Is it for backup purposes? It's generally a bad idea to roll indexes before they're ready, as it can cause long-term degradation in search performance over the data. If you're concerned about hot buckets remaining open for too long without being backed up or closed, it would be better to set the maxHotIdleSecs to something like 86400 (1 day).
The purpose for my question is for backup purposes yes. I would like to have a predictable roll-over of hot buckets so I know that data in the hot buckets is no older than 7 days, as an example. The maxHotIdleSecs seems only to be working when the maxHotBuckets has been exceeded. Ie this is not predictable.