Depends on how its been looked after while it's on the deck.
We have aircraft been parked since March that can fly immediately because we have been doing care of maintenance and flight ready storage procedures.
On the other hand if we had aircraft that have been parked since March that the owners have refused to pay for any maintenance/preservation. Some of these will require deeper more in depth inspection and possibly engine removal. So this can take a while.
Another thing to note is that they may hit the time limits for certain maintenance checks whilst parked up e.g. 24 month inspection. Whilst not necessarily accruing airframe hours.