From my experience, it may depend on what is being changed. Adding synonyms to vocabulary is fairly instantaneous. However, other things take longer to change. Usually, things are updated by the time I've switched tabs in the logical model or refreshed the tab where I'm testing my questions. However, I'm not sure if it is those specific actions that make the logical model update or simply the time that passes while doing those actions.
Quick update. Defining packages is instantaneous as well.
However, hiding fields and master items require you to refresh the Insights page where you are testing your questions. This is likely because that dropdown suggestions is cached in some way.
