It may be non-linear. I guess I am not patient. If it takes up to ~40 seconds I just wait and don't context-switch; if it takes more than ~3 minutes I switch to another work-related task; but if it's in between -- I tend to check the e-mail, or the news, or something like it, and then 15 minutes later "Oh shit! My build\test is done, and I completely forgot I was doing it!"