Is it possible to do a same-day border bounce through Chiang Khong?

Chiang Mai Visa Run goes to the Lao border almost every day.

If they can't get you out and back the same day, they won't even take you

You might check one or two border run companies from Chiang Mai, looks like same day out/in possible. or

As Brandon said, if you have a valid multi-entry visa and are just activating another entry on it you can get out/back the same day with no issue at Chiang Khong or Chiang Saen

BUT

If you're trying to get a new free 60 day entry stamp, you're going to stay out as many days as they tell you. (Usually overnight but sometimes 2 days)

The guard will tell you when you stamp out how long you need to be out before you can stamp back in

Also keep in mind if you have a entry/stay history of free entry stamps they can also tell you that they'll let you out by land but you have to fly back in,

So you make sure you find out from the guard when you stamp out what your restrictions about getting back in (if any) are

Not if you're trying to enter visa exempt. But if you have a valid visa then you can return same day without issue.