According to the Oxy-Rush nanoware, a character with it can hold his breath until it runs-out. It does not give rules for them actually running-out though.
The only metric for that as far as I can tell is the rate at which the transient is nanites are filtered out-of the body :10% per day. The "Hold Breath" ability lasts even when the cyberware has reduced effect, thus it lasts until the cyberware is working at only 24% efficiency. If the character took no wounds, that would take over a week (7.5 days, 180 hours)
Anyone have their own limits on the functionality of the Oxy-Rush nanites?