As part of daily sanity the rebalance in with 10 empty buckets, the time increased from 4.5 minutes to 5.3 minute, between builds 835 and 857. This is an increase of 48 seconds over 4.5 minutes or about 15%. This is readily reproducible.
The node 10.5.3.44 is the one being rebalanced in.
Logs from both runs are attached, please let me know if there is more information I can provide.