ADC variable reference voltage
Your design requires surge currents, as the ADC grabs charge for the conversion behavior. Thus the resistors, along with parasitic capacitance, need to implement a fast timeconstant, fast enough to settle to at least 0.5 degree C during the sampling interval and also during the grab-some-reference-charge as each bit of the successive-approximation-conversion occurs.

One Tau of settling provides 8.6dB improvement in measurement. Thus 10 tau, provides 86dB accuracy (other errors also exist; you must identify and manage those other errors), or nearly 13 bits.

By the way one Tau settling is NEPER.