Wireless Stick inaccurate deep sleep wakeup timer

When I put my Wireless Stick into deep sleep with a wakeup timer, the duration of the sleep is inaccurate.

When I set it to sleep for 30 minutes it wakes up 13 seconds too early.
When I set it to sleep for 2 hours it wakes up 63 seconds too early.

I have tested it with 2 different Wireless Sticks, and the results are identical.
I also tried it with a CubeCell AB01 and the sleep timer works perfect.

I have tried compiling the program with both PlatformIO and Arduino IDE, and the results are identical.

I used this code example to test: TimerWakeUp.ino
I am using this Wireless Stick: Wireless Stick

I was not able to find any information regarding this issue.
Does anyone have an idea what is causing this? Or even better does anyone know how to fix this?

Thanks in advance


I think I found the answer here: https://www.esp32.com/viewtopic.php?t=3715

The internal clock on the ESP32 is simply inaccurate.