Project size is medium (175 hour project) or large (350 hour project). The length of the project 10-22 weeks is something you need to specifically talk to your org about if you want something other than the standard 12 week project length.
The orgs have designated the size of project they expect with each project idea on their Ideas list. When submitting your proposal you should be sure to match the size project they have listed. If you think the project should be smaller or larger then you must talk to the org before you submit your proposal to see if they agree.