Yes, you can - at anytime with no impact.
see my previous answer here:
https://learn.microsoft.com/en-us/answers/questions/60635/healthmailbox-cleanup.html
You can delete them all with powershell: ( or just a few if you want using powershell or ADUC
Get-Mailbox -Monitoring | Remove-Mailbox
Make sure you also read this and give the necessary permissions so the AD objects are removed:
https://learn.microsoft.com/en-us/exchange/troubleshoot/administration/remove-mailboxdatabase-cannot-remove-health-mailboxes
Otherwise, remove the AD objects manually
Then restart the Microsoft Exchange Health Manager, MSExchangeHM service on each 2019 server to recreate them.