For a 5400 RPM drive, worst-case rotational latency is one full rotation: 5400/60 = 90 rev/sec, so ~11ms. Average is half that (~5.5ms). If you also need to seek (yes, we'll definitely need to move on both axes in the worst case scenario requested, likely all the time), 2006-era datasheets show average seek around 11-12ms, with full-stroke seeks around 21-22ms. So worst case total access: ~33ms.