A cycle date is the date you purchase the number, and would get billed for that number.
Every month the date is the same, and you will be billed on the same date.
If you have multiple numbers and would like to get billed for all number on the same date, You can change the date changed to one single date also.
You can view your current cycle date and also change it from the Number info page.
If you would like to change the billing date for all your Virtual numbers then please watch video