Hello,

The problem of measuring a resistor with a time constant RC is
accuracy of the capacitor. You could obtain very good precision with
measurement of the period of a monostable 555 or 74121,
one millionth with a sufficently large counter and quartz stability.
But the exact value of capacity is at best 5%. So accuracy is 5% !
A few bucks digital multimeter gives you a better precision without pain.
There is sense to build a measuring device only to obtain a better
precision.

Regards.