Q:

Does the order of citation ([Kir10, HZK09] or vice versa) matter?

I am currently writing my bachelor's thesis in Computer Science. When I have a sentence
It was shown in [Kir10, HZK09] that ...

does it make a difference if I write
It was shown in [HZK09, Kir10] that ...

instead?

A:

Some styles require multiple citations to be in alphabetical or numerical order.  For example, APA style requires that citations be in the same order as they appear in the references list (that would be alphabetical order.)  Other styles (e.g. the Council of Science Editors) require that they be given in chronological order. 
You need to check with the style guide for the style that you're following to see what is expected. If you're writing a journal or conference proceedings article, the instructions to authors should tell you what is required.  If you're writing a thesis or dissertation, there are likely to be institutional policies that specify a particular style.   
In LaTeX there is a package called "citesort" that will sort your citations.  There is also a "sort" option for the natbib package that does this job.  

A:

First thing to do, is to check to see if there is a style guide for citations with your university and your supervisor.
If there isn't one, make sure when you choose an in-text citation style - keep consistent.
At my university, when I was a student (until last year), the rule was to use the first one in your example, the reason was to show a citation to the most recent works relevant to what you are citing.

