IRS
I really can't remember...and I suggest you e-mail Airbus to get the correct answer.
Yes, it's true, the FCOM states that anything over five seconds puts the IRS alignment into the "Full" mode. Yes, it's true there are no moving parts in the IRS system (except for maybe the OFF-NAV-ATT switch :> :> :>).
But, the IRU system, when turned off, goes through a self-test process, and a position memorization process that takes some time...I don't know how much time...like maybe five seconds, five minutes...I simply don't know. Again, ask Airbus.
At my old carrier, we were told to, when executing the Securing Checklist (where you turn off the IRUs and shut down the airplane for the night) to delay cutting power to the aircraft for at least two minutes after you turn off the IRUs. In other words, you're done flying for the night...putting the aircraft to bed...thinking about that cold beer or two...don't be too quick to shut down the APU right after turning off the IRUs. Give them a few minutes to 'do their thing' after turning them off, before removing power to the aircraft and heading for the bar.
I realize I haven't answered you question, except top suggest that you contact Airbus for a correct response.
Tom