555 timer giving unexpected output (astable multivibrator)
To start with C2 has nothing whatsoever to do with timing. It simply serves to decouple one of the internal thresholds.

Second, the output period for this configuration is

$$period = 0.693  \cdot 2 \cdot R3 \cdot C1$$

which works out to about 65 &micro;s (15.35 kHz) for the component values shown. I don't know why you're measuring 700 Hz. If you changed C1 to 150 nF instead, then the period would be 977 &micro;s (just over 1 kHz). Either way, this is too fast to see, so the LED will appear to be continuously lit.

If you want to see blinking, you need to increase the values of R3 and/or C1 by a couple of orders of magnitude. 10k and 10 &micro;F will give you 140 ms (about 7 Hz).