<p>Is it ok if 2/3 of my LORs are from people not at my university that I only spent the summer with? One was a professor that I did an REU with at a good university last summer, and the other is a researcher at a major national lab that I spent this summer with. My concern is that I only worked with them for 10 weeks, if they write good letters will grad schools care that it was for a short amount of time?</p>
<p>They should be fine. The fact they were not at the same school probably helps you more than it hurts you - more diverse opinions. The fact that they knew you for a short period doesn’t really matter as long as (1) they spent a lot of time working with you in that time and (2) your other LOR knew you for a while. Most 2nd and 3rd LOR’s come from profs who only knew the applicant for a year, maybe just a semester.</p>