Not for complete projects, but only for some tasks. Some clients need bugfix which may take 5-10 hrs a week. There are other clients who request a few hours of work a week. However, such clients are rare! and such tasks are usually ones for experts! I suggest you start your own project and gain experience in it.
I understood that you are hoping to work 5hrs a week on some smaller tasks to earn something extra, but also to gain experience.
In reality, 5hrs a week is very low output for most clients. You will be able to find clients (1 out of 30 maybe) who have such demands but don't expect to have constant work. Put yourself on the client's side: what kind of work is 5hrs a week on a software that has LOT of users who discover new bugs.
So I'd say you will be able to find the client who needs urgent work on a bug that only you know how to solve it. How realistic is this?
And yes, you can find those on the freelancing sites.
Instead of this, if you want to gain experience working when you can and how many hours you can, then start making your own software. You will gain experience for sure and you can work when you can. You will not earn money doing this, but you can also monitor freelancing sites to see if any clients has posted a small task that "only you can complete".