Reviewing through your inquiry:
However was wondering what Jive does in this call that takes so long. Is it also synchronising some unrelated accounts? Disabled users? It seems too quick for all accounts and too slow to be just the one account.
You might find the following section of the Jive documentation helpful - Synchronizing LDAP Users
Though, essentially, when this option is checked, each time a user logs into your instance a check is made with the information stored in your LDAP system to confirm that the current federated profile fields match what is stored in your external system.
Thanks Jesse, but I was more after what specifically is done in terms of LDAP sycnc when one user logs in.
I can kick our developers, indeed we have a ticket, but whilst slightly slow login is annoying it isn't yet top of their list of important things to look at.