maurycy@gimel cpython (fix-remote-debugging-writer-prev-timestamp e867c1d?) % cat repro.py 
import _remote_debugging

w = _remote_debugging.BinaryWriter("/tmp/o.bin", 1000, 0)
try:
    w.write_sample([(0, [(1, 0, [(42, None, "f", None)])])], 5000)
except TypeError:
    pass
w.write_sample([(0, [(1, 0, [("a.py", None, "f", None)])])], 6000)
w.finalize()

class C:
    def collect(self, frames, timestamps_us=None, **kw):
        print(timestamps_us)

_remote_debugging.BinaryReader("/tmp/o.bin").replay(C())
maurycy@gimel cpython (fix-remote-debugging-writer-prev-timestamp e867c1d?) % ./python.exe repro.py 
[6000]