Evohome: What triggers the update to the TRVs

I am just getting my EvoHome ready to install with a mixture of HR92s and HR80UKs and have a few of them sync'd on the bench so I can just check how its works.

I notice that when I change the temp on the TRV it updates on the controller in near real time..

BUT.. When I change the temp on the Controller, its takes a few mins to update the TRVs.. And when it does it does them all at the same time.

At one point, one of my HR80s had "Sync" on the display, and updates were happening in real time.. But once that went away, it went to the standard behavour where updates would takes several minutes.

I am sure this is normal(?), but just want to understand the mechanism for doing this? Does the Evohome transmit at set times (like every minute).. Or does it do it at X seconds after you make a change?

I just want to understand this, as I have 18 valves to sync and I am going to be doing a lot of running around to check they are all working?

Thanks in advance

Jon