Everybody else will act normal and all prior evidence of their existence will also persist like normal.

Edit: For clarification, the people are actually missing but everybody is essentially hypnotized to not notice. Even if specifically asked about the missing people they will pretend like everything is fine. So everybody goes on about their day normaly.

I guess for most people it would be pretty much immediately if their significant other isn’t there in the morning and for some fringe isolated cases it might take forever.

I guess best case for me would be around 4 hours on a work day during lunch break seeing a big crowd of people when it would finally click.

Worst case would be probably 5 days when I’m mostly working from home office.