The accuracy of RTC depends on several parameters: e.g. type of crystal, the temperature condition, Cin, Cout, Rf and Rd of the oscillation circuit.
The build-in resistors Rf and Rd are fixed within the RTC module.
Recommended value of Cin and Cout is from 10 to 22 pF.
Cin and Cout values include floating capacitance due to the wiring. Take care when using a ground plane.
The crystal oscillation stabilization time depends on the mounted circuit constants, floating capacitance, etc., and should be decided after consultation with the crystal resonator manufacturer.