As you know such Power bank run with 3.7V internal voltage so they have to raise voltage up to 5V thru a DC-Boost component (usually 92% efficiency) so as the P = U x I law apply you can remove a big 30% to the value displayed on the case of all USB power banks (or the 18650 batteries) to get the final "5V" result.
If you use the 2 x 18650 TOMO version with 2 x 3500mAh 18650 (I guess it's the highest value possible in such battery size and it's some Panasonic or LG battery that own the record if I remember) you'll get 7000mAh max and then you'll have to remove 30% (power law plus the DC-Boost not 100% efficient) and you'll get around 4900mAh enough to run the Xiaomi a "big" half day, so yes I think your 14H estimation is correct if you use very good batteries.
If you want to be 100% solar you'll also have to size your solar panels capacity so they can both reload the batteries AND power the camera AND do both things also when weaver is bad/rainy/cloudy so the minimum is to double or triple the theorical solar cell power capacity.
So your solar panel capacity will have to be able produce enough power to do it let say if they have light enough to run at 25% of their max capacity for example.
And to do all this calculation the "good thing" is that your camera always use same power on a 24H cycle, but not exactly as it will vary depending how long IRLed are active that use +50mA, so in winter it will eat more energy on a 24H cycle than in summer.
But problem with the usual USB Solar panels is that they use DC-Boost/DC-Buck and have no MPPT technology to increase power efficiency. (as PWM technology that is less effciient than MPPT).