After you have created an alert it will appear on your alerts dashboard. On this screen you can customize how you will be able to receive your email alerts. In the below image you see my alerts dashboard in which I have requested that Google send me alerts to 6 different niche topics.

When you click on the gear icon in the upper right corner, as highlighted in green in the above image, you will receive a pop up that allows you to set the delivery times of your alerts as well how they are received, see below image.

It is totally up to you as to what time you wish to receive your Google Alerts. However I recommend that you receive all alerts in a single email, to avoid an over-crowding of your email inbox. Personally, as seen in the below image, I have it set to receive my alerts at most once per day. You can also set that at once per week.

NEXT UP = More specific settings for each alert