Tool for measuring the frequency of a crystal oscillator
If the flashing looks irregular to you, then it's waaaay too unstable for a clock, and something is wrong. A divided crystal will look stable to the naked eye. 

Use your meter's Hz function by all means, but on the buffered crystal output or high up on the divider to get reasonable resolution, not the 1Hz output. 

Once it looks stable, then you can compare it to various time signals that are available depending on where you live.  In Europe, there are 16kHz and 60kHz broadcast as time signals, and in the UK broadcast 198kHz is stable enough for clocks. Or if you have a 1s GPS output, compare the phase of the two with a two channel scope over a long enough period, minutes, hours or days.