I feed my russian in the morning, and he just randomly eats all day. But that's his schedule, and she's probably used to having a special time where shes fed 20 minutes a day is great, as much as she can eat in 20 mins
since russians 'hibernate' half the time. They eat as much as they can when they are awake. Its normal.. they have to in order to survive.. When you pick her up, she should feel like a rock about that size.
What kind of food and what kind of enclosure? I feed mine weeds and leaves and let them eat as much as they want. Babies were in 4x8 outdoor pens all day and 100 gallon tanks at night. Older ones are in outdoor 8x24' enclosures and eat whatever they want all day.
No need to restrict them unless you are feeding the wrong foods in an small indoor enclosure, and even then its probably not going to be an issue.
I feed her mustard and turnip greens, kale, collard greens, Timothy hay randomly, carrot maybe once every 2 weeks and grassland tortoise pellets sometimes, I try to mix it up, she is in a small indoor tank, 2 ft by 3ft, which I know is too small but I'm looking into a table.