The way I do it is have a couple users on First Release and that way we can see when the new features show up. Unfortunately Microsoft doesn't let tenants know when a feature arrives, they only announce it is rolling out. Unfortunately this "rolling out" can take weeks or even years so it is very hard to plan with any certainty.
Once I do see a new feature I prepare educational materials (typically video) for my users and post them.
OK with first release you get the updates first and most of the time they are pushed directly as you have choosen to have them First.
for the other people in your organisation it is hard to say it can be as short as 3 weeks with a max of 3 months as far as i know.
Blocking is a no go. Compare it to windows updates which is on premm here you have full control but Microsoft always advices you to have the latest Updates. In Office365 they are sure to push you the latest updates..