Your question is not clear, but let's assume that you are trying to add a multifield feature to the "date and time" CF model component.
Before you start coding or anything, you'd need to do some investigation. Create a new CF model, and then author a "Single line text", out of the box CF model component, into your content fragment model... save it, and create a new CF. Edit the CF to include a single line of text. Next, take a careful look at the node structure in CRX/DE.
Moving next, go back into the CF model, and update the "render as" to "render as multi-field". Head back into your CF and add some some text using the multi-field UI. Immediately take a look at the CRX/DE; Take note of how additional nodes are generated when "render as multi-field" is selected.
If you wish to enable date and time with "render as multi-field", you'd need to somehow work your magic to have the same node structure as the "Single line text" CF model component, "render as multi-field".