If your only gone for a weekend then dont worry. Your fish wont suffer going from Friday to Monday with out being feed. Those feeder blocks can contaminate and foul the water.
you need to be more concerned with evaporation than feeding unless your going to be gone for a period of 1 week or more. With SW
as the water evaporates the SG
increases so its important to try to maintan the water level. You dont have a neighbor that you would trust with the key to your house for the time your gone for a week or more? Pre measure the food into small cups and label them for the days they are to feed and you should have a good idea as to what your daily or bi-daily evaporation is that you can premeasure evaporation top off and place in jugs also labled for the day they are to add. Then all the person has to do is come in and feed the approprate labled cup and add the approprate amount of water. Hide the rest of the food so folks dont feel inclinded to give the fish more.