In this case the there are defects from Installation, but also damage from the Variable Speed Drive.
Regulated inspections are annual and testing on a three yearly schedule.
The damage from the drive emissions is of concern and can managed. Energy savings from dropping just 0.02 Ohms is quite significant.
The main issue with Electrical Preventative Maintenance is resources, and many facilities don't have the Skilled labour to test every motor circuit right away. By targeting larger Motors on drives will have the biggest impact on reliability as these tend to have the highest defect rate.
Higher reliability will come from this exercise, reduce reactive maintenance allowing more resources for the rest of your motor assets.
Regulatory requirements state a three year schedule but in 3Phi experience many defects are from installation, so the faster you get them tested the more reliability & energy savings you will return.
You should aim to get your facility tested in the first 12 months, then repeat to get rid of the installation defects. Now your reliability has improved move to a more targeted approach focusing on Motors that have high number of starts or longer start times.