Question about New-ManagementRoleAssignment - Impersonation" -Role:ApplicationImpersonation

Hello, 

I have a question regarding this command

New-ManagementRoleAssignment -Name:"Reddoxx Impersonation" -Role:ApplicationImpersonation -User:RdxMailDepotImporter@contoso.local

Goal:   

we need this Command on our Exchange 2013: 

3rd party tool needs to "import" some mails / mailboxes

can we grant access only to one designated mailbox or database?

Is it possible to switch this "on"  for e.g. 3 days and switch it later "off"   Which command can I use for it?

Thx, Best Regards