How accurate are tide predictions?
Why is there a difference between your tide prediction and the prediction at ...?

The tide data are average values based on astronomical tide predictions and do not take into account the effects of strong winds, atmospheric pressure, rain, floods and other meteorological events.

You should never expect a prediction to be better than 30 minutes.
Just a change of wind direction may change the tide more than this.
Also the official government predictions are just average values and may have significant deviations from the real tide data.
It varies very much with the location, but many research studies have shown that a variation of more than 20 minutes is quite frequent.

Please read how tide predictions work:
https://en.wikipedia.org/wiki/Tide

If you really need a higher accuracy, you should not use an app like this or any of the tide predictions available on the internet.

Please read the app Disclaimer!