The interest payments on Earns are calculated on a daily basis and paid out on the 1st of every month. After the interest payout is made, it will be added to your total available balance and you can withdraw that interest amount at any time (withdrawals are subject to Lendingblock checks and withdrawal fees).
For example, if you create a 1 month Earn with the balance in your account on the 27th day of the month (and there are only 30 days in that month), then the interest for the 3 days will be paid out on the 1st of the following month. The interest for the remaining 27 days will be paid out on the 1st of the next month.