Pluto SDR uses the RAKON RXO3225M crystal oscillator with 25 ppm stability over its operating frequency range of -40 to 85°C.
When operating in the GHz range this 25 ppm is not spectacular, so if absolute stability is required then a GPSDO should be used, for example a unit from Leo Bodnar. These excellent units cost almost as much as the Pluto SDR.
You must modify your Pluto hardware [Link].
When starting Pluto an extra pane is added to the receive DSP with the current temperature. 24 hours' data is available via the Download button. The format is CSV which can be opened with programs such as Excel.
And example of a chart which you can create with Excel is shown below.