The Payday Boost is a recurring monthly deposit. On the date you choose, the amount you select will be added to your upcoming collection. This total is then collected in the next available Wednesday collection, and debited from your bank account early the following week (usually on the Monday). This means that your boost will leave your bank account a little later than the day you select, so it’s worth bearing this in mind when setting this up!
You can make changes to your boost any time in Settings > Payday boost.