SN74LV221A-Q1: maximum value restriction of Rext and Cext

The SN74LV221A-Q1 itself does not have a limit and supports, in theory, arbitralily large time intervals.

But the length of the time interval is determined by charging the capacitor through the resistor, and waiting until the capacitor's voltage reaches a certain threshold. If you are using a large resistor and/or a large capacitor, then the leakage currents of the components can become large enough to affect the timing.

The graphs in the datasheet show component values that are known to work, and do not go above 10 ms. I would not use a resistor larger than 1 MΩ, and check the capacitor's specifications; in general, foil or ceramic capacitors have lower leakage currents/higher isolation resistance.