Xiaohong and Xiaolan agreed to meet in the library. Xiaohong's watch was 5 minutes behind, but she thought it was 10 minutes behind. Xiaolan's watch was 10 minutes behind, and she thought her watch was 5 minutes ahead. Who was late when they met? How long does it take for early arrivals to see latecomers?
小红和小兰约定好在图书馆见面，小红的表慢5分钟，而她以为慢10分钟，小兰的表慢10分钟，她以为自己的表快5分钟．她俩会面时，谁迟到了？早到的多长时间才见到迟到者？
<result>20</result>