Amazon has a number of hoods with fan timers (I searched "fan timer" in the "range hood" category). Note that some hoods have convenience timers that don't turn off the fan. The Cosmo hoods specifically say "fan timer".

Some Venmar/Broan hood fans have a 5 minute auto off timer but iI think you will have difficulty finding your desired 20,40, 60 minute option. Some advise to start your fan prior to cooking to establish a good room airflow to the exhaust, i find the 5 minute adequate most times.

If it takes 60 minutes post cooking to clear your kitchen of smoke, either your fan isn’t powerful enough, or you’re doing something really wrong with your cooking. A powerful fan with the correct capture area just needs to be on a minute or two past the cooking vapor production. Re-examine your ventilation setup.

Where do you put the food left overs, the dirty dishes, etc after you cook and eat? Reach up and turn it off. As you clean up........ ! .The noise of ANY fan running for 60 minutes, no matter how quiet, would make a sane person insane. Get a timer if you can't hear it.

Think too, that if this were a BIG issue for most? It would be standard on most if not all hoods.. Which it is not : )

The marketplace sorts this stuff out pretty quickly....

I think some are now controlled via an app...you can choose when to shut them off and even fan levels. Super helpful for those who are disabled.

https://appliances.monogram.com/us/specs/ZV950SDSS#features 

One risk with using a timer is that it could turn your exhaust off while it is still needed and so result in unhealthy VOC's left in your home.

Our range hood exhaust is controlled by our home automation system (Control 4, but others can do the same). If it has been on for 2 hours I get a notice on my phone and then again at 3 hrs, 4 hrs, etc. That way I'm reminded to turn it off if it's been left on accidentally (since ours is silent on Low and someone unnoticable on Medium this is easy to do).

If I know that it's no longer needed I can turn it off from my phone. Otherwise I go to the kitchen to see what's going on - like my chef daughter-in-law creating something amazing. :-)

I have a delayed shut off (i.e., timer) on my current Miele hood and I absolutely love this feature. It has a 5 and 15 minute option, and this covers all of my needs perfectly. I use the feature daily, and will insist on a similar feature in my upcoming build. Even if there is no effluent left to clear, it is nice to help evacuate residual heat. Off the top of my head, some brands offering delayed shut off features include Miele, Thermador, ZLine, Blue Star, Viking, Best, and Proline.