Two successive GBT's have different targets and nbits. Target increases until a block is found. nbits won't be used until the next block and depends on this block's timestamp:


getblocktemplate

{
...
"previousblockhash": "0000000000093658813abd9f0c97b05cb5e3d23594b17c8abf27919312158af3",
"target": "0000000000b4d61573b036be175f295d6cd1e1d9c839e58cc85db34cd0760100",
"mintime": 1571004547,
"curtime": 1571005288,
"bits": "1b2a1d9c",
"height": 7
...
}



getblocktemplate

{
...
"previousblockhash": "0000000000093658813abd9f0c97b05cb5e3d23594b17c8abf27919312158af3",
"target": "000000000124ab302ef78bfb86628340481f85b4f0e6808b8ef587995ef7ced8",
"mintime": 1571004547,
"curtime": 1571005363,
"bits": "1b4b0ce2",
"height": 7
}