How do I merge two 'Date and time' attributes?

I have two date and time fields that I like to merge. From one DateTime I need the date, of the other DateTime only the time. for example:

1/1/1970 14:30

and

11/05/2017 00:00

How do I merge these two such that I can get 11/05/2017 14:30?

Thank you in advance