It doesn't matter, but you should have a good background or have taken enough related coursework.

Different mentors will expect different ranges of weekly hours, but this is usually flexible from week to week, depending on deadlines.

International students can do research work on campus as part of their Curricular Practical Training. Curricular Practical Training (CPT) is only available to F-1 students who have not graduated and who have been enrolled on a full-time basis for one full academic year (i.e. fall and spring.)