In OpenSearch how to find the total time it took for index creation?

Versions (relevant - OpenSearch/Dashboard/Server OS/Browser):
OpenSearch 2.12

Describe the issue:

I’m using reindex option to copy 1 Million documents from one index to another.
How can i find the time it took for index creation? I’m working on knn index, hence knowing the time it takes to Index is important for my tests

POST /_reindex
“source”: {
“index”: “Index_A”
“dest”: {
“index”: “Index_B”

I tried using GET /Index_B/_stats
But everything under indexing like index_total & index_time_in_millis both is 0

3 nodes cluster

Relevant Logs or Screenshots: