To convert your varchar into a datetime, I would recomment Try_Convert() if 2012+, if not just Convert() would do the trick provided your data is reasonable.
try_convert(datetime,Timestr,103) -- returns 2016-12-28 16:39:01.000
To use Format()
Declare @Timestr varchar(25) = '28/12/2016 16:39:01'
Select DateTime12 = format(try_convert(datetime,@Timestr,103),'yyyy-MM-dd hh:mm:ss tt')
,DateOnly = format(try_convert(datetime,@Timestr,103),'yyyy-MM-dd')
,Time12 = format(try_convert(datetime,@Timestr,103),'hh:mm:ss tt')
,Time24 = format(try_convert(datetime,@Timestr,103),'HH:mm:ss')
Returns
DateTime12 DateOnly Time12 Time24
2016-12-28 04:39:01 PM 2016-12-28 04:39:01 PM 16:39:01