Inertial Navigation Old Timers/Experts

[A320Slave]

Hi all,

Just a quick question and i apologize if this has been asked in the past.

If the INS was not updated at the gate first flight of day, can the INS reset itself to be accurate after departure, in flight, with an FMS (no GPS on board)? If so, can it 'right' itself within 10, 20 mins after departure? In other words, if the INS can 'right' itself while underway, how long would you anticipate accuracy? And/or can INS be considered accurate if not reset in a stationary position?

In further words, if the pilots werent able to update their INS at the gate (whether too lazy or behind schedule) and the INS was off by 1,000-2,000-3,000 ft at the gate, can they rely on the INS to update itself in flight and/or even perform an update in flight to be accurate?

Please explain for either answer.

Thanks in advance...