It is a gas price issue.
According to EtherScan you are using:
0.00000002 Ether (20 Gwei)
According to EthGasStation.info this is below the safe low at the moment:
Unless you want to get involved in a difficult game on cancelling old transactions, I suggest you create a new Ethereum account and try to deploy the contracts from there with higher gas price.
The error tells you exactly what the issue is. In the line
you are using a variable which was not declared previously. You can add
var adoption = artifacts.require("adoption");
to the top of the file if you have the adoption contract defined in that Truffle project. If you haven't defined it there, you will have to copy it over ...
Your hunch is correct.
__DateTime______________________________ is a marker for linking in Solidity bytecode. This marker will be replaced by DateTime library smart contract address when the smart contract bytecode is linked (should be 32 bytes if I recall correctly).
The full deployment process looks like this
Deploy libraries, get their smart contract ...