The first thing is to figure out what the number means for your database. Is it milliseconds since January 1st, 1970 or something else.
At that point, I would write a program to load the number into a java.util.Date object and output it. (You could do this with a calculator if you had to, but I can't imagine why you want to do that. Accounting for leap years and the like would be a nuisance.)
If you were using JDBC to get the SQL TIME, you could call rs.getTimeStamp and output that directly.