Well, 600 square feet can be a studio but it's by no means a small studio. It's enough space for a perfectly comfortable 2 bedroom apartment. (Or 3 if you squeeze.)

For a single room, if that towel holds a gallon it should work fine for an overnight humidification job.

It's very effective for humidification, the difference is immediately noticeable. The room is probably 100 square feet, I'm only humidifying it at night, so by your calculation it should take only about half a gallon of water which is probably what fits on a towel give or take.