@tigeriseye Greetings, for basic exercise they can stay in for as long as 5-30 minutes. For best results the eggs come in three sizes, Large (38mm), Medium 30mm, Small 20mm; and they are held within by the vaginal wall and pelvic floor muscles. My eggs come drilled so that they can be stringed for easier releasing and/or for adding weights to it. You may opt in having them charged.