This article applies to Classic Commerce. (Looking for Contextual Commerce documentation?)
Most companies by default choose to be paid Twice Per Month. With this setting, you are paid every 2 weeks with a 2 week lag. This means that sales from the 1st to the 14th would be paid around the 30th/31st/1st; sales from the 15th to the end of the month are paid around the 15th of the following month. If a payment date falls on a weekend, the payment will be made the Monday following the weekend.
If you have set your payment cycle to be monthly, then on or around the 15th of each month, you will be paid for any sales from the previous month.