You can use the index setting index.lifecycle.origination_date to set a custom "age" for the index, so that if you were to reindex, you can tell ILM that it is a certain age without waiting for that long.
Here's a blog post about it: Control the phase transition timings in ILM using the origination date | Elastic Blog
And the reference documentation: Index lifecycle management settings in Elasticsearch | Elasticsearch Guide [8.0] | Elastic