How long does it take for the Earth to rotate on its axis

You may think you know the answer to this one.

 You need a length of tubing like a narrow pipe or cardboard cylinder (if it’s going to be dry).

 Sight a bright star like Sirius or Rigel or Vega etc, etc. through the tube and firmly fix the tube in that orientation.   This will take some ingenuity. You need to have the star dead centre in the tube.   When it is, note the time.   The next night get to your tube at least 5 minutes earlier than you took the sighting the previous night and wait until the star is dead centre in the tube again.   Note the time.

 If its not clear the next night, wait until it is and then divide your time by the number of days that went by between sightings.

Don't use Polaris as your sighting star as it goes nowhere.   On the other hand, as a permanent garden feature, it could be useful to check for Polaris visibility it you need to do a polar alignment on your telescope!