Using time-based indices covering soecific periods through the name and querying through an alias means that data will be colocated by time. Indexing old data may be more expensive as you target more shards but you pay this price only once. When you query using a time period you know a lot of shards will not hold any relevant data which will generally speed up queries.
In old versions of Elasticsearch querying all indices used to be expensive, so Kibana used ways to determine the correct indices to query before running the query against just these indices. Initially this was done by calculating index names based on timestamp range but later this was replaced with a call to an API which provided the timestamp range for each index (removed issues with data being in the wrong index). In more recent versions Elasticsearch has improved a lot and this is no longer necessary. Querying an index that does not have any data within the timestamp range is now quite quick and efficient. I therefore do not think you need to worry about querying all backing indices through an alias.