Every time the clock reaches 6PM, the game always send a notification about the Daily Reward which can start to get annoying especially if the player knows or learns that they arrive every 6 PM making this unnecessary. Other daily events such as the Party Boat and Competition Center don't do this.

It's annoying that there's no way to disable the Daily Reward notification. The closest way to turning it off is either disable the notifications for The Sims FreePlay within iOS' or Android's settings, or by turning off the Notifications setting through FreePlay's Options. However, this will also disable other notifications such as the building being finished, Sim finishing work, Sim waking up, items that have finished growing/baking, etc.

Do Not Disturb on iOS can also disable the sounds from the Daily Reward notification although you'll still get the Notification.

Edit: It seems Do Not Disturb disables the alert sounds from Notifications but not the actual notifications themselves. This will disable the sound that plays although you'll still get the Notification.