It doesn't need to be proctored. It would be easy to start a remote clock and the solution needs to be in by x minutes after the start. It can even be pretty generous. The idea is presumably not to see how fast they can sprint but just put some time-boxing in place so some people aren't taking days.

People can get help of course but that's going to be the case absent effectively a remote proctored assignment. And now you're back to effectively in-person.