What don't you like about those results? I'm not seeing anything that looks out of line.
A bare GPS receiver will always have jitter on the timing output. The magnitude of the jitter is related to the clock speed of the internal processor and the state of the ionosphere at the current moment. The spec for the NEO-7N timing receiver is 30 ns RMS. The NEO-7M doesn't even have a jitter spec. Old GPS receivers had jitter specs as high as 1 us on the 1 PPS output, yes, microsecond!
If you have the numerical data that you used to create the graphs, calculate the average value of the period. You should find that the result is really, really close to the correct value. The longer you collect data, the closer the average will get.
The jitter coming out of the GPS receiver is the reason that GPSDOs exist. The disciplined oscillator filters out the jitter and gives you a clean(er) signal.