I Got a Dark Patch on Both my Arms from Leaving 10 % Glytone Peel on for 24hours

Keep the area well moisturized and protect it 100% from the sun until the skin is completely healed and back to normal color. Glycolic peels are usually quite superficial and will almost always heal without problems. If you are concerned, it would be best to see a dermatologist who specializes in cosmetic treatments to give you guidance in doing this type of treatment.