You are correct. A qclock is even more inaccurate when you factor in the multiple markers that people use (e.g. dates, minutes, post numbers…). That's why it's nearly impossible to predict what's going to happen, but fairly easy to confirm that an "event" was intended to happen. That's why "news unlocks the map".
It's fun to build qclocks to see what "might" happen or to get a general feel for "the plan" or to educate yourself on topics Q points us towards or to be amazed at how precisely the plan is being orchestrated . However, the odds of accurately predicting the day an event will take place in the future, using the qclock, is right up there with winning the lottery.
That said, I'm still a qclock addict.