Then you have a lot of indices created at basically the same time every day, which is why they take time to allocate. I would recommend either consolidating a lot of these indices into fewer larger ones, which would mean fewer indices and shards would need to be allocated at the same time, or switch to using rollover for indices that does not need to be updated. Using rollover allows you to create new indices based on age or size which means they will not all be created at the same time.