Pickle it
 

lots of diesel and pull out all of the upholstery

Know that no amount of effort will save the electrical....

Cut and inch off, resolder a ring and in a few months of use the whole strand is green...

As far as wood, fresh kills...salt preserves.....don't worry there...just get it dry because the added weight of intrusion can collectively be enough to break the boat.

As far as the motor....

Get a lot (4/5 gallons each motor) of trans fluid, denatured alcohol and wd 40.

Within an hour or two of refloating..start working on the engines. Pull plugs and dist.....completely out...plus vc's. Compressed Air and trans fluid liberally across the valve train...big mess....suck out everything in the pan through the dipstick.....don't mess with the drain plug or you will prolly have to change the pan....

Once the valve train looks good.....douse in denatured alcohol....and refill the pan with trans fluid....

Cheap stuff....you're gonna use a lot...

Then, over fill the motor with trans fluid in the pan and wd straight down the throat of the intake

For those that have missed my prior thread about wd 40, wd stands for "water displacer"

Crank.....crank......crank....let the engine blow it out..."then refill through the carb/ intake and do it again.

Then again.....

Then again...

Obviously, you need to remove and drain the oil filter between steps...sorry for not mentioning til now.

Drain, replace filter dist and plugs....fire it up...With cheapest available screened oil.....viscosity does not matter.

Now....for the naysayers.....if the dist is in for this, there is no chance to rinse away the water that has collected in the valley.....so...just do it.

After five minutes, shut down and drain hot......refill..... and drain same oil filter through whole operation....then refire for another five...

Now....make a filter change and add more garbage oil....

You will do this three more times.....cheap oil, new filter.....five minutes each
Finally....new filter, good oil.

Run for 20 with someone watching the gauges...

All good?

New filter, new oil, new plugs.

Now run for an hour....no load.

Hopefully, you have someone doing the same on the other engine simultaneously.....

Once here, change everything again including cap and rotor and carefully load the engines......but stay away from hole shot and wot.

After an hour or more, come back and change all again....including the spare dist modules that you took out with you.

Order new starters, new alts.

Externally bathe entire engine bay and motors.....with more wd.

If the sinking was in less than one atmosphere, drives are fine but might as well cange the oil there too. If more, the job just got bigger....

Trim pumps, brackets for same, batteries, switches for same, shore power charger, house panel......anything and everything electrical is phucked...

This is not an impossible job, but you have to work fast after you refloat...

Sorry."
 

Now to answer your original question....

The timing means little within a couple of weeks....

Important is how soon you begin to save it once it is floated....which should be immediate!!!

Great advice from a very fart smeller .
PS: One atmosphere equals 33' and is the area of the most pressure change underwater .

Preserve the motors so you can take them apart later. Filled a brand new motor with fresh water a few years back. Flushed and changed the oil 4 times in a day. Couldn't sleep at night so I decided to rebuild the next day. When I took it apart I found water was still in there that would have wiped out the motor in an hour if used.