How to set only time part of a DateTime column ?

I have column of type datetime

I want to set only time part now for constant date

i.e i want to set it to "01/01/2000"+ now() where 01/01/2000 is always taken and add the hour and minutes to it

for example

if now is 29/06/2016 16:45  i want to save 01/01/200  16:45