How to convert a VARCHAR DD/MM/YYYY H:MM:SS AM into datetime and then to Json date?
somewhat old but still ...

https://stackoverflow.com/questions/10735447/is-there-a-way-to-convert-a-varchar-to-datetime-in-sql-server-2008

convert(datetime,'24/05/2012 09:56:06',103)


set your column containing the varchar as the second parameter - 103 is for the --/--/---- format ..

I tested above command against a SQL Server 2014 and it works when you omit leading zeroes - and also with AM / PM addition so perfect for your case

The only thing that needs some more work is your desired addition of the timezone, but I highly suggest adding that only for display, not in the actual database