Cache Expiration doesn't follow Drupal conventions

Drupal 8 convention for $expiration on set() is based on unix_timestamp() but this module expects expiration in TTL form like Redis (e.g. seconds till live)

CacheBackendInterface outlines:
* @param int $expire
* One of the following values:
* - CacheBackendInterface::CACHE_PERMANENT: Indicates that the item should
* not be removed unless it is deleted explicitly.
* - A Unix timestamp: Indicates that the item will be considered invalid
* after this time, i.e. it will not be returned by get() unless
* $allow_invalid has been set to TRUE. When the item has expired, it may
* be permanently deleted by the garbage collector at any time.

However the calculation in redis/src/Cache/CacheBase will always return the permTtl if you pass in a unix_timestamp() per spec because unix timestamp will always be larger than TTL based on time difference from time().
1 if ($expire == Cache::PERMANENT || $expire > $this->permTtl) {