Monitoring employee attendance

My company wants to check employee are meeting their contractual obligation of being in the office X number of days. Let's just say they are required to be in the office for 4 days of the week.

We already have access/swipe controls so the data is being collected, but not used or interrogated in any meaningful way. Our privacy notices/policies do state that access is monitored for site security purposes. However, using this data to check attendance would likely be a new purpose.

They don't want the full access logs, only if Person A was in the office on three days of the week )they are not interested in their movements within the building or that granular level data). Only the Exec team would see this data.

This would need a DPIA and an update to the privacy notice. Are there any other considerations you think should be made? If it helps, they want to take a sample of 2 months data from the end of last year and use this as the 'sample'. There's a clear legitimate interest in making sure employees meet their contractual obligations, but is there anything else worth considering?

Thanks