This isn't really how contract law works. There may be minor details that are not specified in the contract but unless it can be proven in court that those details were actually within the contemplation of one of the parties and connected to his or her decision to enter into the contract, their absence would not be sufficient to nullify the contract.
A contract is an agreement, so it stands to reason that if the parties do not, in fact, agree, there is no contract. The piece of paper we call a contract is, in fact, only a (strong) evidential tool to help the court figure out what the parties agreed.
> Far stronger reasoning (for example) is that a contract must spell out time, which is a special property of contracts because (for example) 1000000 years is virtually never an acceptable period for which to fulfill on your end of a contract.
How is this "far stronger reasoning"? It isn't even reasoning at all, because there is no existing rule that a contract must spell out time, so it's simply an untruth. Unless you were suggesting that the court create a new rule out of nowhere that all contracts must spell out the time for performance or else become void. A court would obviously never do that in light of the huge disruption it would cause.