Electronic – How to add a digital pulse generator to a simple LED circuit

Just for grins, here's a 555 astable with a duty cycle variable from about 1% to 99%, and if you choose to build it, C2 should be hooked directly across pins 1 and 8.

Diodes are not ohmic. Resistors have a linear relationship between current and voltage. That is the relationship described by Ohm's law which you used in your question. Diodes look like this:

We normally model them as a simple voltage drop when they are forward biased and an open circuit when they are reverse biased. If more precision is desired, we sometimes model the forward biased state with a voltage drop and a resistance. However, what you have computed is not the same as this resistance. Your calculation fits a line between the origin and your present circuit's operating point, giving a much different number.

To say that your LED has that resistance is misleading as if you change the current, the voltage will not change proportionately.