At what point (after clams die) are they ok to eat
Clams are exceedingly perishable; there is no length of time after they are dead that you should eat them.  They should always be killed as part of the cooking process.

They may open (they are naturally filter feeders, and open to try and feed and respire), but if tapped should close indicating they are still alive.  If they don't close, discard.

Clams do not have tongues.  They have a siphon, and a foot--not sure which you are referring to.  The siphon is normally trimmed off if it is large, but the foot may be edible (although sometimes tough and not palatable) depending on the type of clam.