How strict are the time validation rules?
If the next block is mined more than 2 hours after the current block, would this not stall the blockchain?
It doesn't break the rule "Full nodes will not accept blocks with headers more than two hours in the future according to their clock."
Nor does it break the rule "Must be strictly ...
I think you have a misconception about what this clause means:
Full nodes will not accept blocks with headers more than two hours in the future according to their clock.
You appear to be interpreting this as, if a new block is more than two hours later than the previous block, then do not accept it. That is incorrect. This clause is not about gaps in time ...
The SHA256 hash algorithm produces what looks exactly like a random number in the range 0 to 2256-1 (1.1579208923731619542357098500869e+77). Each of those values should be equally likely.
So if you produce a large number of these by altering the data to be hashed, you cannot steer the results and most of the results will be a large number.
Some of the ...
Bitcoin difficulty is not determined by the "number of zeros", but none the less the Bitcoin genesis block would satisfy a difficulty target substantially higher than might be expected. This doesn't really mean anything in the scheme of how the system operates, it's just a curiosity.