If you notice that Group creation via HC API or Panel interface is taking extra long time then please first verify Group creation manually using Exchange PowerShell command,
 
New-distributiongroup -displayName "TestGroup" -name "TestGroup@abc.com" -OrganizationalUnit "OU=MyOrg.com,DC=ad10,DC=lab03,DC=com" -Managedby "Mark@abc.com" -type "Distribution"