How can I get the DateTime of when bitcoind last received a block? Is there a command to get the DateTime of when bitcoind last received a block?
No, there isn't.
getblockcount can only get the number of blocks in the best chain, but not the last received block.

You might need to write a new rpc to get the last received block. 

First, add a new data structure in main.cpp and record blocks received order in ProcessBlock().

Second, write a rpc to print out that data structure.