Yes it's OK to do planks everyday.
The more planks or planking exercises you do the more calories you burn and the more weight you'll lose.
When planking everyday you not only lose weight but you also build muscles and you work your abdominal muscles as well.
Planking is one of the best exercises to build muscle, tone your stomach and lose weight.
When you do planking you burn more calories than you would doing push ups.
Although push ups are also a great calorie burning exercise the planking is much better but you'll get the best results when doing both pushups and planking exercises everyday or at least 3 to 4 times per week.
There's no harm in doing planking or any other exercises everyday and the more you exercise the healthier you become.