Are we assuming that the satellite is going to stay in the same orbit? The atmo drag will constantly be applying pressure on the cubesat so that its orbit will always being decaying.
I don't think atmospheric drag at 400km is large enough to decay the orbit by half the vertical height of the ISS in half a cycle, though. The ISS itself with it's comparatively huge surface area does orbital reboosts only about once a month or so.[1] Also, my original comment was quite simplistic - a launch with a negative delta-v with no other course correction would result in an elliptic orbit with the same apogee but a lower perigee (and the other way around with a positive delta-v.) Orbits are tricky that way.
