You can parse time and date strings with java.text.SimpleDateFormat. What you want to do is add two time intervals, I think, since adding two times doesn't make that much sense (what is Oct 31 + Dec 25?) Some things to watch out for:
1. Set your date format's time zone to UTC, since you don't want to rassle with time zones.
2. I would extact the long time value from the parsed date and work with that. For instance you can add two of them together to add the two intervals. While you could turn around and use the date format to format the result as a
string, like "05:00:10 + 01:35:05 = 06:35:15", watch out if the hours exceed 24 -- it will want to take you from 1 Jan 1970 to 2 Jan 1970! It's simple to format the time interval manually: