Import-Module ExchangeOnlineManagement

Connect-ExchangeOnline -UserPrincipalName admin-m365@client.onmicrosoft.com

Get-Mailbox -RecipientTypeDetails RoomMailbox | Set-MailboxCalendarConfiguration -WorkingHoursTimeZone 'Eastern Standard Time' -WorkingHoursStartTime '08:00:00' -WorkingHoursEndTime '17:00:00'