Mining of the Genesis block testnet? Bitcoin 0.14
I want to try mining first genesis block, a new time, but don't know how to start
testnet

used to create GenesisH0
https://github.com/lhartikk/GenesisH0
To mine the testnet genesis block you would use.

python genesis.py -z "The Times 03/Jan/2009 Chancellor on brink of second bailout for banks" -n 414098458 -t 1296688602


If you want to create a new genesis block run the following with your own time and leave out the nonce, you will be generated a new nonce.

python genesis.py -z "The Times 03/Jan/2009 Chancellor on brink of second bailout for banks" -t 1501755824


Here is what I get when running the above command, it will just take some time to find a block.

python genesis.py -z "The Times 03/Jan/2009 Chancellor on brink of second bailout for banks" -t 1501755824
04ffff001d0104455468652054696d65732030332f4a616e2f32303039204368616e63656c6c6f72206f6e206272696e6b206f66207365636f6e64206261696c6f757420666f722062616e6b73
algorithm: SHA256
merkle hash: 4a5e1e4baab89f3a32518a88c31bc87f618f76673e2cc77ab2127b7afdeda33b
pszTimestamp: The Times 03/Jan/2009 Chancellor on brink of second bailout for banks
pubkey: 04678afdb0fe5548271967f1a67130b7105cd6a828e03909a67962e0ea1f61deb649f6bc3f4cef38c4f35504e51ec112de5c384df7ba0b8d578a4c702b6bf11d5f
time: 1501755824
bits: 0x1d00ffff
Searching for genesis hash..
183984.0 hash/s, estimate: 6.5 h
nonce: 835054047
genesis hash: 00000000ad3d3d6aa486313522fdd4328509feefe8c37ead2a609884c6cbab92


To add your new genesis block to the Bitcoin testnet update the src/chainparams.cpp file, also delete any checkpointData entries on the testnet as those no longer apply to your new testnet chain.