At least once a day, and whenever else I feel like it. I don't think losing the diet mentality has anything to do with whether or not, or how you use a scale.
Weighing whenever I was tempted to, actually helped me lose the diet mentality and the punishment aspect of weightloss.
The less often I weigh, the more I obsess over how every bite might affect the scale. Instead I decided to treat and view the scale/weighing like other emotionally neutral tools/activities.
When I treat it like checking my teeth in the mirror after lunch, to see if I need to floss the spinache out of my teeth, doing it once a day, or even twenty, is only obsessive and harmful if I allow it to be.
I've decided to treat my weight like my hair length. I get to decide when and if I need to change it (grow my hair longer, or cut it shorter), and I don't ever have to feel bad about myself because my hair is shorter or longer than I'd like.
Seeing the number on thexscale doesn't have to be an emotional experience whether you do so once a year or thirty times a day.
Now that I weigh whenever I'm curious, I think about the scale a lot less than when I tried to avoid or limit my use of the scale.
Even when I first decided to do this, when I was weighing myself every time I ate, drank, or used the bathroom, I was still thinking about my weight and the scale a lot less than before.
The number on the scale really isn't important to me, but the changes are. If I'm suddenly up 5 lbs that can mean I'm retaining water. During some times a year that can mean swollen ankles and wrists and it can aggravate my arthritis. Seeing the weight gain sooner rather than later, and drinking extra fluids to flush the weight gain prevents the blood pressure and arthritis aggravation.
Checking my weight daily is no different than brushing my teeth, monitoring my blood sugar, or using moisturizer on my hands and feet to prevent calluses and cracks.