You're making vague statements so lets make sure things are clear. There are three possible outcomes for the policy assuming no one violates the curfew. Either every single person cancels their social events, some fraction of people cancel their social events, or every single person moves their social events to earlier. Obviously the only reasonable assumption is that some fraction of people will cancel, some fraction of people will move theirs earlier, and some fraction will ignore the curfew.

I'm going to assume you agree because only a literal retard would believe every single person is going to move their social events hours earlier, and it would be pretty shitty to assume you're retarded. So if we know that at least some people are going to move their events and some are going to cancel, the question that needs to be answered is "what fraction of social events will be cancelled?" This isn't a question we can outright answer without data, but we can at least think about it in an organized way.

Would you still go to a party after you get off work at 4:00 if you had to leave at 5:30-45 to beat the curfew and there was travel and prep time to think about too? And if you get off work at 5:00 then including prep and travel time you're talking about a 15 minute party. So it turns out this policy almost completely eliminates social gatherings for working people on five days out of the week. That alone seems like it could be pretty significant.

Now, exactly how effective this is likely to be requires a ton of data and analysis, but I think I've shown pretty clearly here that a naïve opinion of "people will just move them up a few hours" is unsupported. Turns out to make the claim that it won't work you're almost certainly going to have to do day or even weeks of research and statistics.