receiving, for a first item and a first user, first data comprising a first score representing a predicted likelihood that the first user will order the first item within a predefined amount of time;

determining a first set of features comprising features related to past voice notifications sent to the first user, past voice notifications consumed by the first user, and past orders of items associated with corresponding past voice notifications consumed by the first user;

determining a second set of features comprising features related to orders of the first item when a voice notification corresponding to an order of the first item was sent and orders of the first item when a voice notification corresponding to the order of the first item was not sent;

generating, by a first machine learning model, a first scaled score using the first score, the first set of features, and the second set of features;

determining, based on the first scaled score, that a first voice notification is to be sent to a device;

generating a first activity map comprising a first number of columns representing respective time slots and a first number of rows representing respective weeks, wherein a value of a first cell of the first activity map represents a first number of occurrences of a first event type during a first time slot and a first week associated with the first cell;

generating, by inputting the first activity map into a convolutional neural network comprising at least a first convolutional layer and a first pooling layer, first feature data comprising a down-sampled representation of the first activity map;

generating, by at least one fully-connected classification layer using the first feature data, a first vector, wherein each element of the first vector corresponds to a respective time slot, and wherein a respective value of each element of the first vector represents a respective predicted probability that an event of the first event type will occur if the first voice notification is sent to the device during the respective time slot;

selecting a second time slot of the first vector based on a first predicted probability associated with the second time slot in the first vector; and

sending audio data comprising the first voice notification to the device associated with the first user during the second time slot, wherein the first voice notification includes a prompt to remind the first user to reorder the first item.