1/
https://etn.nanopool.org/ +
https://etn.spacepools.org/ > 50%
2/ A block can only be added at the end of the blockchain, so they are always mined in order, that means the dates are simply wrong. A blockchain has no time consensus, so the dates dont need to be accurate, the only "time consensus" a blockchain has is the heigt. Thats why updates will be released at a block height X and not at a time X. Im not sure how they measure the timestamp on a transaction but i asume the miner just puts his server timestamp in, which dont has to be accurate at all.
I assume you thinking about 51% attacks. With those attacks you can replace the block by mining with more then 50% hashrate, but you keep them secret. So you wouldnt see the increased difficulty anyway ,because the solved blocks would not be released to the global blockchain. After time X you will always have the longer blockchain (because you solved more blocks) wich is accepted by the global blockchain, so you would just suddenly see the end of the blockchain removed and replaced with something else. But even these added blocks will be in chronological order.
So lets say a big company which owns a lot of hashing power makes a deal with nanopool (or they get hacked by the company). You would first see a huge decrease in difficulty, because nanopool would be not releasing their blocks, but they could keep the miners in the dark about it, give them all the money they want, because its gona be reversed anyway. Then they make their scam deals and release the longer blockchain, which would be accepted globaly. Not to easy but since their is a lot of centralization with ETN mining (most of it because of lack of knowlege) it is not impossible. In the beginning of ETN mining one pool even had 97% of the hashing power.
TL;DR The timestamp is not reliable, only the block height is and its impossible to add blocks inbetween
