Take homes can & ought to be timed.
I've had the opportunity to do this fornat twice and I think it works well.
Here's how it works: They ask you to pick a 3 hour time window to work on the project. You pick the time. They send you the project prompt in an email right at the beginning of your time interval. You have 3 hours to read the prompt, design, implement, test a solution. If you miss the deadline, project counts for nothing.
Both the times I did this the prompts were absolutely doable in 3 hours. They were the kind thing you could do in about 2 hours if you had the ability to read the project prompt ahead of time and think about it for a few days.
Personally, I work well with time constraints. This format feels closer to a workday where mid-afternoon you might challenge yourself to finish a task before 5pm. Its a lot less pressure than having to juggle a conversation and having your code scrutinized in real time.
It forces a real time constraint that keeps you from piling time into something you just don't know.
Its hard to cheat, and it also forces the company to make the task achievable in the time frame. This format forces them to realize when the task is too big for anyone to finish in the time.